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Buzzing behind! (at higher rpms)

 
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StienbargerR  



Joined: 28 Oct 2005
Posts: 1362
Location: Richmond, IN

PostPosted: Mon Apr 27, 2009 6:36 am    Post subject: Buzzing behind! (at higher rpms) Reply with quote

Hey guys,

I do recall a few discussions about the rear ends being noisy, but I have much luck finding them.

Anyway, like the thread says, My car makes a buzzy vibrating noise in higher rpms. I recently inspected the transaxle area, and found a loose fuel pump. I tightened it, but I am still getting alot of noise/ vibration at about late 4k-5k rpms. I checked the torque on the cv bolts, they all seemed fine. I also have re greased the cv's pretty recently.

Any suggestions of what I should check? I must add that I do not currently have the sound deadening carpeting in, but the noise is so loud I'm sure that it wouldn't make much of a diffference.

Thanks,
Ryan

edit- Should also add that this buzzing is not the type of buzz that a running fuel pump makes.
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1978 924 NA
-250lb lowering springs, Euro Pistons
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Smoothie  



Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)

PostPosted: Mon Apr 27, 2009 9:48 am    Post subject: Re: Buzzing behind! (at higher rpms) Reply with quote

StienbargerR wrote:
I must add that I do not currently have the sound deadening carpeting in, but the noise is so loud I'm sure that it wouldn't make much of a diffference.

We might have to agree to disagree on that.
I've noticed that the sound deadening makes a huge difference.
I was noticing my normally noisey transmission just the other day. Can hear it clear as day, and I have the factory sound deadening, and the carpeting, plus a thick padded removable carpet piece on top of that. That probably adds up to 1.25" of sound insulation.
Drove it a bit a couple years ago with nothing back there after finishing my repaint and it was crazy noisey.
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'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox
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RC  



Joined: 25 Mar 2007
Posts: 2636
Location: Australia

PostPosted: Mon Apr 27, 2009 1:00 pm    Post subject: Reply with quote

Wouldn`t be the exhaust vibrating/ resonating?
Have had problems with mufflers and resonator not supported sufficiently, flexing, and breaking internally or around end flange.

Agree that it is noisier without the sound deadening but not dramatically and nothing that a few extra watts through your woofers can`t overcome.
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joecitizennn  



Joined: 12 Sep 2005
Posts: 2096
Location: no mans land

PostPosted: Mon Apr 27, 2009 1:10 pm    Post subject: Reply with quote

Tranny noise is common in our cars. I have noticed diffirent levels of noise between cars with equally good transaxles. Gear lash, mount condition, wear and especially sound matting have effect on this aspect of the 924. I am so used to it I seldom pay it any mind. I have been through several junk porsches and hand picked a quiet tranny that has great synchros . Its sometimes luck of the draw.
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StienbargerR  



Joined: 28 Oct 2005
Posts: 1362
Location: Richmond, IN

PostPosted: Mon Apr 27, 2009 5:43 pm    Post subject: Reply with quote

Hey thanks for the input. I guess I will put the carpet back in for starters. I will definitely check the muffler/ exhaust system. Some of you may know I had an accident in it last year and haven't driven it much since, so maybe a hanger got loose or damaged.

Ryan
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Nobbi  



Joined: 24 Aug 2006
Posts: 1379
Location: Germany

PostPosted: Mon Apr 27, 2009 8:32 pm    Post subject: Reply with quote

Do you have the right amount of oil inside of youre tranny ?

Did you put back on the half-round metall brackets on your drive shafts?
You took them off to re-grease .... In the right place?

Did you lost some balance-weight on your tires ?

Do you run the right tire-pressure?

to be contiued.......
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NA 924 - april/1977- 4-speed-audi gearbox.
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ideola  



Joined: 01 Oct 2004
Posts: 15548
Location: Spring Lake MI

PostPosted: Mon Apr 27, 2009 9:33 pm    Post subject: Reply with quote

Nobbi brings up an excellent point about the tires being a possible culprit. On my daily driver BMW 325i, I had a really loud howling sound that I was almost certain were wheel bearings...sounded just like 'em, and the car was at 160K+ miles so it would have been plausible. However, it turned out to be the tires, believe it or not. A quick and simple rotation fixed the problem.

Take a look at the tread of your rear tires. If you took a hit, it's possible the car is out of alignment and the tires are wearing unevenly.
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924guy  



Joined: 29 Dec 2003
Posts: 2088
Location: Port St. Lucie, FL

PostPosted: Mon Apr 27, 2009 10:09 pm    Post subject: Reply with quote

also check the heat guards between the body and tubes... sometimes they can rust loose a bit and make a wicked noise that sounds somewhere between a screaming cat and a bumble bee... it resonates through the whole car and makes it sound like its coming from the rear sometimes, when its actually right under the shifter area...
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78 924
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StienbargerR  



Joined: 28 Oct 2005
Posts: 1362
Location: Richmond, IN

PostPosted: Tue Apr 28, 2009 4:15 am    Post subject: Reply with quote

924guy, Im not quite sure what exactly you are talking about, but the description of the sound fits the bill. could you expand a little bit about where the screws are?

thanks,
Ryan
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ideola  



Joined: 01 Oct 2004
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Location: Spring Lake MI

PostPosted: Tue Apr 28, 2009 7:39 am    Post subject: Reply with quote

I believe he is referring to the heat shield that is directly above the torque tube, in the tunnel, and directly between the driver and passenger seat. It is not fastened with traditional nuts or bolts. There are tiny studs welded to the body, and the panel fastens with these funky flat-style speed nuts. If the speed nuts are corroded and have gone missing, the heat shield will come loose over time, and could be vibrating against the torque tube.
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924guy  



Joined: 29 Dec 2003
Posts: 2088
Location: Port St. Lucie, FL

PostPosted: Tue Apr 28, 2009 12:02 pm    Post subject: Reply with quote

ideola wrote:
I believe he is referring to the heat shield that is directly above the torque tube, in the tunnel, and directly between the driver and passenger seat. It is not fastened with traditional nuts or bolts. There are tiny studs welded to the body, and the panel fastens with these funky flat-style speed nuts. If the speed nuts are corroded and have gone missing, the heat shield will come loose over time, and could be vibrating against the torque tube.


what he said... ^^^^
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78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
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StienbargerR  



Joined: 28 Oct 2005
Posts: 1362
Location: Richmond, IN

PostPosted: Wed Apr 29, 2009 5:38 am    Post subject: Reply with quote

oh, gotcha. I will check that out too

Thanks,
Ryan
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Nobbi  



Joined: 24 Aug 2006
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PostPosted: Wed Apr 29, 2009 11:35 pm    Post subject: Reply with quote

....one more point: Does it make that noise also when parked ?
and does it make a diffrence if you press the clutch pedal ?
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NA 924 - april/1977- 4-speed-audi gearbox.
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StienbargerR  



Joined: 28 Oct 2005
Posts: 1362
Location: Richmond, IN

PostPosted: Fri May 01, 2009 12:47 pm    Post subject: Reply with quote

Nobbi,

It never makes noise parked, and no noise till past about 3,000 rpm. I put the carpet back in and it helped alot. I also noticed that my passenger side rear tire is wearing abnormally, so I think it is out of alignment. Also, it could probably use some fresh oil in the transaxle.

Thanks for the help all.

Ryan
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