Can't locate this noise

[hughnohoo]

Just 25k on the clock on my 2005 A4, and I have , for the last 1000 miles or so, what seems to be a belt squeal, but I don't think thats what it is.

Read the threads about the problematic harmonic balancer and its rubber seal that goes bad, and sure enough, saw that the pulley had a wobble, so thinking "this is it !", took it into the dealer and had the pulley replaced (out of warrenty of course so it ran almost $1000).

Ran quiet for a day or 2, then the noise popped up again. It seems to happen more often ( and is loudest) after the days start-up, and for the first few miles, but it does happen when at run temp too, just not as bad or as loud.

The noise is intermittant, meaning it does not always happen, and I cannot make it happen on demand, so my mechanic has not heard it (been there twice with no noise for him to hear).

At its worst, sounds like a metal on metal bearing going bad, and it kicks in usually while in 2nd gear, and just as its about to shift into 3rd. Haven't heard it at WOT, but maybe the exhaust noise drowns it out, dunno. After motor warms thoroughly, instead of a metal screech, it just makes a rattling brrrrt sound, very briefly and just before the shift into 3rd.

After the harmonic balancer was replaced, and I still had the noise, I changed out both drive belts, as the dealer left the originals in place, but noise is still there.

May be belt related (like maybe the idler, or tensioner, or a/c, water pump or alternator (it happens whether the a/c is on or off tho), or it may be something in the motor (hope not tho !). Only does it under a load (won't do it revving the motor in the garage), and kicks in around 2500 rpm or higher under moderate throttle in second gear. Have not heard it from first to second, or from 3rd to 4th. Cannot hear any bearing noise during idle from a/c, water pump or alternator.

I would take it back to dealer and let them keep it overnight to see if they can hear the noise in the morning, but as I said, it does not always happen, so that could be a waste of time too.

If anyone has suggestions, or advice how to narrow it down (my friend refuses to ride in the engine compartment ), I would appreciate it.

[c4c5specialist]

HI there,
Its most likely the AC belt tensioner.

All crankshaft pulleys have some wobble to them, and unless its shifted, you can leave them alone.

Allthebest, c4c5

[NORTY]

I thought that too, until the OP said," it only happens with moderate acel and during 2/3rd gear change."

If it were the A/C tensioner, it would occur in most all gear changes as the rpm would be similar. Since it's an automatic.

[hughnohoo]

While I am not at all sure about the a/c tensioner being the culprit, I'll get the part, and maybe another new belt..have a gatorback on the main drive, but they didn't have that brand for the a/c belt so used another. Heard/read lots of good things about the gatorback so will try one also.
Really busy at the moment, but as soon as I have the time, a week or so, will make the swap and let you know if it was successful. Thanks.


Edit: If anyone is still following this thread, i decided to recheck the rpm at which the noise comes in and its about 3000-3500, and if I go thru the gears manually, I hear the noise in every gear at that rpm. That a/c tensioner is looking more suspicious....

[hughnohoo]

OK, so it took me awhile...but I finally got it done.
Changed a/c tensioner & main belt tensioner, & tried to change the main idler pulley as well, but the parts houses say no such pulley exists lol. Dealer says he can get it, but will take a few days...but in any event the noise is gone so will leave well enough alone!

Thank you to both C4C5 Specialist, and Norty.

Update: 1 day later the noise is back & I guess if it is a belt noise, all that is left is the idler pulley, the alternator pulley, the power steering, a/c , and the water pump...so screw it, if the idler pulley doesn't fix it, I will live with the noise until she blows up.
Thanks anyway guys. :(