All measurements are in decibels. While the decibel as a way of measuring intensity of noise is a complex term, it can be very easily demonstrated. There is an excellent webpage with flash animations presenting you noises decreasing by 3 or 1 or 0,3 decibels. Try it. This will allow you to see the differences between compared cars. It’s essential to realize that decibel is a logarithmic measure which means that relatively large changes in noise level result in little changes in decibels measured.
Then look at this chart to see what's what in terms of noises around us.
The list of cars has been ordered by the noise measured inside the car at 70 mpg (~112,5 km/h). If results were equal, a noise at full throttle was considered - the lower, the better. Source is Edmunds InsideLine full or comparison tests. To put V8 diesels in perspective, two additional cars: Audi A8 4.2 TDI and BMW 745d were measured by Auto Motor und Sport at 100 and 130 km/h. Measurements were then interpolated and floored (rounded down to the nearest integer).
The upper part of the list almost certainly contains the quietest cars on the market today. The lower may not be as representative. Some cars absent here may land somewhere between the ones measured and placed there.
A clear conclusion is that while the top is occupied by very expensive vehicles, it is by no means a necessity to spend a lot of money to get a really silent car.
In case of some cars like BMW 335i and Toyota Prius, more than one measurement was available. Lower results were picked in such cases as one can assume that readings in noise level measurement procedure can much easier be overstated (due to presence of additional noise sources like something outside the moving vehicle during the test) than understated. It's nearly impossible to unintentionally make test noise readings lower in a vehicle cruising at a given speed.
Format is: the rank, the car and noise level in decibels
at 70 mph (~112,5 km/h)
at full throttle
when idling
 | 1. Lexus LS 600h L 58,9 66,6 38,3 Anything this Lexus does, it does it quieter than Rolls Royce Phantom. Not bad! The only car that can possibly beat the largest hybrid is the Maybach. Edmunds InsideLine did a full test of it and... they didn’t measure noise levels! 2. Rolls Royce Phantom 59,0 67,0 40,0 The Queen Elizabeth is where she's supposed to be - at the very top of the list. 3. 2008 BMW 535i 61,2 70,7 43,1 That's a true surprise, to see this Bimmer here. But when one thinks about it for a second, it becomes somewhat logical. The 535i has a twin-turbo petrol straight six. High torque due to charging means little revs are needed to cruise what decreases the noise. And then come the turbines themselves, clogging the exhaust manifold and quieting the car even more. Excellent performance from an unsuspected contender. 4. Mercedes-Benz S550 62,0 66,0 48,0 It was certain to find this car close to the top. 5. Lexus LS 460 62,5 68,3 37,2 LS460 follows its hybrid version closely. 6. 2007 BMW 335i 62,5 76,3 46,9 Like father, like son, the 335i twin-turbo handsome looking brute benefits from the same quietly beating yet potent heart. 7. Mercedes-Benz GL450 62,6 72,5 42,6 Big powerful SUV means there's lots of space and carrying capacity for decent sound insulation. Big V8 in low revs doesn't shout either. 8. 2005 Land Rover LR3 63,0 69,0 Low Softly-sprung LR3 is an oasis of comfort also in terms of noise level. 9. 2006 BMW 650i 63,1 71,5 45,0 A transcontinental grandtourer can growl a bit when floored but has to whisper when not. 10. 2009 Hyundai Genesis V8 63,3 72,3 43,8 Can you recall all those people mocking Korean cars and disrespecting these as cheap and nasty econo-boxes? 11.2009 Hyundai Genesis V6 63,5 70,8 39,6 12. 2007 BMW X5 4,8i 63,6 77,6 46,0 13. BMW 750i 64,0 69,0 45,0 14. 2007 Mercedes-Benz CL600 64,0 70,5 43,0 Jeremy Clarkson calls this car "the new King of the Road" 15. 2006 Land Rover Range Rover Supercharged 64,0 72,0 Low Louder than the LR3. 16. 2009 Audi A4 3,2 V6 64,0 72,8 43,5 Handsome looks, front axle shifted forward, rear-biased quattro, small petrol engines all fitted with turbochargers - very good. And now it turns out the B8 A4 is also very quiet. 17. BMW 745d 64,0 unknown unknown 18. 2007 Jaguar XK 64,2 77,2 45,5 19. 2007 BMW X3 64,2 71,8 40,5 Very quiet for a not that expensive compact SUV. 20. 2007 Lincoln MKX 64,3 72,6 48,4 Same can be said about this Lincoln. 21. 2007 Mercedes-Benz E550 64,4 70,8 45,9 22. 2007 Lincoln MKZ 64,5 73,2 46,9 23. 2009 Lincoln MKS AWD 64,6 74,5 44,0 24. Volkswagen Touareg 2 V8 64,7 71,6 42,6 25. Lexus GS 350 64,7 72,2 39,2 26. 2006 BMW 550i 64,8 69,4 42,7 27. Mercedes-Benz E320 CDI Bluetec 65,0 68,8 45,5 28. 2006 Mercedes-Benz ML350 65,0 69,0 41,0 29. 2008 Toyota Highlander Hybrid 65,0 69,6 42,4 Decent result - the Highlander Hybrid makes sense not only in terms of fuel economy but also the quiet ride. 30. Bentley Continental Flying Spur 65,0 73,0 46,0 You'd expect the big Bentley to fare better, wouldn't you. 31. 2008 Mercedes-Benz C350 Sport 65,2 75,8 43,3 32. 2008 Land Rover LR2 65,3 74,5 42,3 33. 2007 Bentley Continental GT 65,5 72,4 50,4 34. 2007 Volvo S80 V8 AWD 65,5 79,6 44,5 35. 2006 Audi A6 4,2 Quattro S-Line 65,6 70,4 47,5 36. 2007 Mercedes-Benz GL320 CDI 65,8 71,3 46,1 37. 2007 Lincoln Navigator L 4WD 65,8 75,0 42,3 38. Audi A8 4.2 TDI 66,0 unknown unknown Not as refined as its petrol rivals. 39. 2009 Acura TSX 66,1 74,9 41,8 40. 2008 Nissan Altima 3.5 SE 66,2 73,6 41,7 41. 2007 Mercedes-Benz SL65 AMG 66,3 74,0 47,7 SL can be excused by its retractable hardtop, one of the best inventions in car body design. 42. 2008 Toyota Camry Hybrid 66,7 73,1 46,8 (engine on) 42,4 (engine off) Good result for a relatively inexpensive car the Camry Hybrid is, to see it among much more pricey vehicles. 43. 2006 Porsche Cayenne Turbo S 66,8 73,8 42,4 44. 2007 BMW M6 66,8 77,7 58,0 45. 2007 Infiniti G35 Sport 66,9 77,6 41,4 46. 2006 Land Rover Range Rover Sport Supercharged 67,0 69,0 48,0 47. Lexus GS 450h 67,0 73,6 37,5 Disappointing. Its petrol counterpart is much higher in the rank. 48. Audi A8 W12 L 67,0 75,6 44,5 Is it really the ultimate luxury sedan from Audi, so low in the rank? 49. 2007 Cadillac Escalade 67,1 78,4 44,8 Quieter than rap music its stereo plays all the time. 50. 2009 Mazda 6 67,1 80,1 44,1 Mazda 6 fares well in quietness department also. 51. 2008 Honda Accord EX-L 67,3 73,1 44,7 52. 2005 Jaguar Super V8 67,5 73,6 48,0 53. 2007 Lexus ES 350 67,5 74,6 41,0 54. 2008 Cadillac CTS 67,5 82,9 43,3 55. 2008 Toyota Prius II 67,7 70,6 47,2 (engine on) 40,7 (engine off) The lightweight hybrid has no chance of having thick sound proofing, still performs well, most likely thanks to CVT gearbox which can adjust engine revs as precisely as needed and low drag decreasing wind noise. 56. 2009 Jaguar XF Supercharged 67,8 72,5 46,8 In the past, big cats used to tiptoe when moving about. 57. 2006 Volkswagen Passat 2.0T 68,3 71,2 45,8 This is a turbocharged car so same principles as in case of twin-turbo bimmers should work also. They don't. Little sound insulation? 58. Audi S5 68,8 77,2 42,5 The handsome S5 was born to growl so its poor performance can be somewhat excused. 59. 2007 Volkswagen Passat Wagon 3.6 4Motion 68,9 73,3 44,0 60. 2008 Lexus IS 350 68,9 77,9 38,6 Loud. 61. 2005 Acura RL 69,0 71,0 unknown Lots of good things can be heard about Acuras so I was expecting these to fare much better. 62. 2007 Acura RDX turbo 69,4 75,2 41,4 63. Audi Q7 4,2 69,8 74,1 45,0 After achieving scary fuel economy of 11,2 MPG in Edmunds InsideLine full test, the big Audi finds itself quite low in this rank too. The Merc GL450 achieves 15 MPG and is at the opposite end of the list. 64. 2009 Volkswagen Jetta TDI 70,0 72,8 47,7 Very good for a small diesel sedan. The common rail injection smoothers the rattle. Typical for a diesel, high low-end torque allows the car to cruise at low revs and helps too. 65. 2005 Cadillac STS 70,0 73,0 unknown 66. Volkswagen Phaeton W12 70,0 73,0 unknown As the fifteenth child of dr Ferdinand Piëch (yes, he really has 13 children, the 14th is the Bugatti Veyron) this car cries rather loud as for an ultimate VW sedan. 67. 2004 Infiniti QX56 70,0 75,0 unknown 68. 2003 Bentley Arnage R 73,0 75,0 51,0 No comments. This car weight nearly 2600 kg (~5700 pounds), has an engine from a locomotive which barely has to rev to power the car along and yet it finishes last here. |
Late entries - after tidying up the post I realized Volvo XC90 wasn’t enrolled. So quick check places it as follows: the 2003 2.5 turbo is out of business with its 75 dB, the 2005 with Yamaha V8 (68 dB) is placed between Jaguar XF Supercharged and VW Passat 2.0 turbo and the 2007 V8 Sport performs very well and with it 64 dB and 84 dB (cruising and full throttle) lands somewhere after the BMW 745d.
References
2009 Acura TSX
2007 Acura RDX turbo
2005 Acura RL
Audi Q7 4.2
2009 Audi A4 3.2
Audi A8 W12 L
2006 Audi A6 4.2 Quattro S-Line
Audi S5
2007 Bentley Continental GT, 2007 Mercedes-Benz CL600
2003 Bentley Arnage R
Bentley Continental Flying Spur
2007 BMW X5 4.8i
2007 BMW X3, 2008 Land Rover LR2
BMW 335i Coupe
BMW 750i
2008 BMW 535i
2006 BMW 550i
2007 Jaguar XK 2006 BMW 650i
2007 BMW M6 2007 Mercedes-Benz SL65 AMG
2005 Cadillac STS
2007 Cadillac Escalade
2009 Hyundai Genesis V8
2009 Hyundai Genesis V6
2004 Infiniti QX56
2007 Infiniti G35 Sport, 2007 BMW 335i, 2008 Cadillac CTS, 2008 Lexus IS 350, 2008 Mercedes-Benz C350 Sport
2005 Jaguar Super V8
2009 Jaguar XF Supercharged
2006 Land Rover Range Rover Sport Supercharged
2006 Land Rover Range Rover Supercharged
2005 Land Rover LR3
Lexus LS 600h L
Lexus LS 460
Lexus GS 450h
Lexus GS 350
2007 Lexus ES 350
2007 Lincoln Navigator L 4WD
2007 Lincoln MKX
2007 Lincoln MKZ
2009 Lincoln MKS AWD
2006 Porsche Cayenne Turbo S
Rolls Royce Phantom
2008 Mercedes-Benz GL320 CDI
2006 Mercedes-Benz ML350
Mercedes-Benz S550
Mercedes-Benz E320 CDI Bluetec
Mercedes-Benz GL450
2009 Mazda 6, 2009 Mazda 6, 2008 Nissan Altima 3.5 SE
2008 Toyota Highlander Hybrid
2008 Toyota Camry Hybrid, 2008 Toyota Prius II
2009 Volkswagen Jetta TDI
2006 Volkswagen Passat 2.0T
2007 Volkswagen Passat Wagon 3.6 4Motion
Volkswagen Touareg 2 V8
Volkswagen Phaeton W12
2007 Volvo S80 V8 AWD
2007 Volvo XC90 V8 Sport
2005 Volvo XC90 V8
2003 Volvo XC90 2.5T