[ds968]

Not yet, but it's this on this weekend's agenda though...

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[ds968]

Almost sure it's the outer exhaust tip which is a slip-over part on the stock tip, and welded-on . The welding spots did not separate or crack, but something must have happened that's now causing it to "buzz" . It won't budge at all, so it's not as if it's loose , but If I hit the pipe that leads to it with a rubber mallet the resonance is heard clearly, until and if I hold the tip with one hand , or pull it up / push it down slightly while hitting the pipe at which point the buzzing sound stops completely . So I'll have to have it welded in some additional spots I think , which hopefully might stop the noise. Just wondering why it would not make that resonance sound all the time and only does it on deceleration between 70-60 mph, and also at idlle only when fully warm. ??

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[az968]

May have to do with heat expansion and magnifying a vibration in the tail pipe that peaks at that rpm. Is your exhaust tip chrome? I polished my until all the black was off and it looked nice.

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[ds968]

That makes sense . Yes, the overlay tip is chrome. I realize I could have polished the stock tip but I also like the " beefier " shape and look of this one so I'll stick with it .

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[ds968]

Good news , bad news, good news, and possibly really, really bad news :

G : Nothing associated with the exterior of the exhaust system is broken ,loose, worn or touching .

B : The rattle ( metallic buzzing resonance ) seems to eminate from somewhere inside the system ...perhaps a muffler .

G : I still have the blue car's entire OE cat back which is in perfect shape nicely stored under the house so if it is indeed a bad muffler , or something else behind the cat , it'll be a relatively easy replacement .

PRRB : If the cat got toasted somehow , and that's what's actually buzzing , I could be royally screwed ; I believe our cats have been NLA for a long time , and as Flash will tell you , he's tried the only two or three after-market ones available , none of which will pass emissions in CA.


Please, oh please , let it be a muffler ..


( The reason I suspect it could be the catalytic converter is because the sound is more pronounced when the car runs for a while and the engine gets very hot. It happens more on on deceleration at certain RPMs, though even on acceleration it's loudest between 1200 rpm and about 2800 rpm, but almost inaudible below 1200 or above 2800 - I tested those rpm levels and related noise symptoms once again, just a couple of hours ago . Then again I suppose the same symptoms could be the manifestation of something busted inside a muffler ?? )

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[ds968]

Replaced the exhaust today ( catback portion ) . The good news is that the catalytic converter's internals look intact / perfect. So somewhere else along the way , even though not visible when peeking through any of the openings , whether it was in tne resonator, or the muffler there was a problem . But everything's nice an quiet now .

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[az968]

Boy, you could use some good car news about now.

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[ds968]

No kidding, this car is like a never ending PITA .

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[williamoss]

So now for my noise in a standard shift coupe. I was driving along and everything was great. Then just as I pulled into a driveway where my other car is being fixed due to a transmission leak, I heard a very loud tapping noise from under the hood and the central red light (above the speedo and tachometer) came on and the 968 stalled. I started it up, put it into a parking spot raised the hood and could hear very loud tapping noises coming from the top of the engine. Raising the rpms just got louder. So I drove it home slowly; at speeds above 30 mph it seemed like the tapping noise went away but at slower speeds it was there. Got it home called AAA and had it towed to my mechanic. I checked the oil and it was right at the top line so not a low oil level problem. My mechanic guessing as he has not seen nor heard the tapping sound said perhaps an oil pumping issue. WHAT DO ALL OF YOU THINK?

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[ds968]

Now that my exhaust noise is gone, and everything is nice and ( relatively ) quitet, I'm hearing an unusual sound coming from the rear of the car when I accelerate more than usual while in a right hand turn. I don't hear that sound in any other scenarios, whether straight line driving, accelerating or decelerating or at different RPMs , or on left hand turns, or even aggressive / hard right hand turns if they're momentum ones, but if I step on the gas while doing that there is a rumble that's fairly loud . Very smooth, consistent rumble, no vibration at all, and oddly enough it almost sounds like the exaust note is louder on those turns , but I'm pretty sure it has to be related to the rear right wheel somehow ..bearing , or suspension component or something along those lines. Eh, probably a topic for a differentpr new thread , once I test it some more ..

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[az968]

Does your car have LSD?

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[ds968]

No, but the way it's been acting lately it may be ON LSD.

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[az968]

Tire out of round or balance?

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[MCL968]

Could it be your new exhaust pipe touching something in the exhaust tunnel? You didn't hear it before, and now you do, and the only think you changed was the exhaust. I would look there first.

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[ds968]

I looked at that very carefully while the car was up on the hoist , mostly to make sure it's not close enough to the heat shields where it could make contact , so I moved it up and down as far as it would go and it's all clear but I never thought to push it side to side and see if it touches anything . I'll check that out today ,

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[968Syncro]

The typical test for a worn wheel bearing is to compare the apparent noise in a right turn vs. left turn, typically at 20-30 mph so the other car sounds are not so loud.  Since the weight shifts to the "outside" wheel, there will be a difference in sound.  But that should indicate a worn wheel bearing on the left side during a right turn, which is opposite of what you are hearing.   And I am not sure how acceleration during the turn would influence this test, but perhaps acceleration would increase the forces that emphasize the noise during the test.   Perhaps run some more left and right tests, with and without acceleration, it may be possible to rule out a wheel bearing if the noise is conclusively on the inside wheel during the turn.

 

And then there are the CV joints, a worn one will make noise.  But what from I've heard, the CV joint failure is more of a clicking sound, not a rumble.

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[ds968]

I'll take it through the various motions to test that also. But considering how smooth this is, just sounds like a much louder exhaust note when I accelerate in a right turn , the pipe / muffler getting close to something which makes it resonate is a pretty good theory . Would t a tire issue or a cv joint or a bearing problem manifest itself at other times as well as , or cause noise , vibration , or more pronounced problems than what this is ?

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[968Syncro]

Yes, the exhaust theory is more probable, since that was the recent change.   From past experience, a failing wheel bearing may be hardly noticeable unless pushed hard on a right / left curve - the test works best when rolling downhill on a curvy road while in neutral/engine idle and just coasting.  I already ruled out tires since you take really good care of you cars -- old tires will make very annoying and loud noises that get louder with speed (more like a roar rather than a rumble).

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[ds968]

Checked the exhaust system, not close to touching anything no matter how much it moves. I did some search on the symptoms and a lot of info seems to point to a differential going bad . Ugh, here we go again ...this is turning into a $ 20 K annual R & R car .. And I don't mean rest & relaxation ..

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[az968]

Well, the right wheel is the only driven wheel since you don't have LSD.  If the sound only comes from that side, the differential could be a fault, how many miles on this car, I don't think that many? If you have been keeping the diff fluid changed, and you probably have, the diff should be good for a lot more miles, esp the gear set. It could be the roller bearing on that side inside the diff (999 059 066 01). I would think that's not a horribly expensive repair, unless there are more "while I'm in there" things to replace. As Syncro968 suggested could also be a failing CV joint or wheel bearing, or a sticking caliper and you are hearing the pad scrape. May not yet be time for the second mortgage on the house.

 

You might also try an ear plug in your right ear, that will make the sound go away.

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