MFranke

I read an old 928 review written in 1989 from Pirtle's review page. It shows the 928 as very quiet in the cabin, almost as quiet as a Mercedes or even quieter than a modern Prius at highway speed. I try to think back when I had the car in the early 90s and do remember a quiet ride. There was no dynamat or any other extra treatment needed and it was still quiet. These days the 928's interior noise is louder, particularly the rear tire noise.
Bearings are new. My question is what original components can be refreshed to get it back closer to original quietness, particularly the rear wheel area? Suspension parts?

James Bailey

Much has to do with the tires , the agressive cool looking tread patterns which have become so popular are rated as mud and snow tires. The result is they SOUND like the old snow tires !! Also as the tread wears some styles get real noisy and mimic a bad wheel bearing. Much is written on tire racks reviews about tire noise. If you do not drive at high speeds consider lower performance tires with a less fashionable more simple ribbed tread...they are much quieter and wear longer.

hinchcliffe

Find the right tires for noise and that will help largely. I think passenger car highway or all season are the best for noise.

terry gt

I have contential extreme contact tires rated quiet, but there is still a lot of tire noise . Our C5 vette is even louder.How would you install the sound mat. ? and where ?

MFranke

Update: My average decibels on my '88 (per I-Phone app Decibel Ultra, held chest level) are now about 55db idle, 70db @50mph traffic, and about 75db@ 70mph traffic, on an average road (not new asphalt). I know the I-Phone is not the best instrument to use, but as a baseline the noise was mid-80'sdB on highway!!

What did I change, other than noisy fuel pump? Wheels and tires! Wow, what a difference!

Recently, I went from stock 16" to essentially new 18" Panamera 5-spokes wearing Ventus v12s. (I got them from Willhoit who got them off a GT - so thanks to whomever donated these!) I suspect the increased wheel size helps too because my '87's road noise is louder - it has new tires as well, but they are 16s.

I guess I underestimated how the tire noise crept up on me. Now I mainly here wind noise... much nicer than road noise! No dynamat!

SMTCapeCod

The tires generally get louder as they wear, too. Often a big difference from new to 60% or 70% mark.
Good news though, I was going to mention all those hundreds of rubber compound suspension bits meant to isolate vibration and noise...

Nicole

I recently drove a 928 with 25k miles. It was much, much quieter than mine (108k miles). I suspect there are many rubber pieces that have hardened on mine over time, while the low mileage example lived most of its life in a cool garage and went through few warm-up cycles in its life.

MFranke

I would still like to know what these rubber bits are so I can change the ones that make the most difference.

Obviously the biggest rubber bits are the tires. While I greatly enjoy the new relative quiet, even with new wheels/tires it is still not down to the advertised 71dB. At some point the tires will get noisy again, and maybe that is when the other rubber bits come into play?

dr bob

Start with transmission and engine mounts. That way the big mechanical driveline noise generators are isolated from the chassis/body. The rear wheel bearings are isolated by the suspension bushings, and impacts by the big rubber isolators on top of the shocks. There are rubber bushes in the mounts at the forward ends of the control arms that isolate the body right under your butt from some of the longitudinal impacts.

Dictys

Here is some data for comparision, this is measure at 130 kmh which is around 80 mph.

1995 Audi A6 2.8 69 Db
1995 BMW 728i 66 Db
1995 BMW 523i 66 Db
1995 Honda Civic 1.5i VTEC-E 72 Db
1995 Mercedes E230 74 Db
1995 VW Golf CL 1.6 74 Db
1995 VW Golf Cabrio 1.9TDI 73 Db

1996 Citroen XM V6 69 Db
1996 Ford Mondeo 1.8GT 73 Db
1996 Mercedes C280 69 Db
1996 Mercedes E230 T 71 Db
1996 Opel Astra 1.6 16V 73
1996 Renault Megane 2.0 16v 76 Db

2000 Ford Mondeo 2.016V 69 Db
2000 Toyota Corolla 1.6 76 Db

2002 VW Golf 1.9 TDI 72 Db

2003 BMW 730i 66 Db
2003 Toyota Camry 2.2 71 Db
2003 Toyota Corolla Compact 1.4 73 Db

2006 Audi A6 2.7 TDI 70 Db
2006 BMW 520d 69 Db
2006 Mercedes E220 CDI 69 Db

2008 Mercedes C250 CDI 69 Db

2009 BMW 330d 68 Db
2009 Honda Civic 2.2i-CTDi 72 Db
2009 Ford Ka 76 Db
2009 Ford Mondeo 2.5 Titanium S 70 Db
2009 Mercedes C350 CGI 68 Db
2009 Opel Astra 1.9 CDTi 72 Db
2009 Porsche Carrera 73 Db
2009 Renault Megane dCI 69 Db
2009 Toyota Auris 2.0 D-4D 71 Db
2009 VW Golf 2.0 TDI 72 Db

I'll measure my 1990 S4 later and post that up

StratfordShark

I'm running Yokohama AVS Sports on 17" wheels, and they're much, much quieter than previous Bridgestones.

I need to replace driver door seal which is really only source of irritating noise as it's right by my ear! It's the original, and I can see the window is not a great fit at the top rear where the seal has sort if widened out whereas it's tight fit to glass on passenger side

Dictys

Do you mean the upper window seal? rather than door seal?

I did mine last week, both the window and door seal, you need to remove the door trim and the inner upper door trim to do both. Once the door trim is removed you can unplug the electrical connectors and remove the hex bolt holding the door restrainer. This allows you to fit the door seal without doing anything stupid like cutting it.

The upper window seal was a pain, mainly due to removing the old seal bead and getting the thrust wedge located. Do the thrust wedge first to postion the window seal, then use the fat end of a screwdriver to roll the seal into the bead.

Both of these fixes did a lot to reduce the wind noise, still some above 80 mph. Road and exhaust noise seems to the main issues with my car at the moment.

MFranke

I hadn't thought of transmission mounts. When the car starts getting louder, it is usually from the rear. Most if that was tires as my recent tire change demonstrated, but I'll have to inspect the transmission and bushings.

StratfordShark

Sorry did mean the upper window seal.

Replaced the door seal a while back, and I did do stupid thing and cut it! The connectors at door did not want to disconnect easily, and I was wary of breaking something. The cut seal glues together so well I couldn't find where I'd done it without forensic examination.

Thanks for your tips on installing the window seal - will copy and keep.

Tony

Where do you measure the sound from? ear level? on the ctr console?

makes a difference.
I will have to measure mine again....its noisy, but i always wear earplugs when i drive. The grooved concrete beltway i drive 90% of the time is horrible with my "tready" BFG KDWs. I spend too much time around noiser engines the way it is so the ear plugs take that annoying edge of the road noise. Ive got dynamat and padding stuffed in the rear wheel arches as well.