5CHN3LL

Running with no belt should be done VERY briefly...but if your squeak is constant with the belt on, it should only take a few seconds to verify whether it's present with the belt off.

If it doesn't squeak when beltless, further troubleshooting can be done with the engine off... Spin each accessory/pulley by hand to figure out which one is squeaky...

williamr91

I have the same sound...took to my local dealer to investigate/do a post purchase inspection. I asked how much a belt change would be (ever though its very easy) and they quoted me a modest $150 installed...including the belt, so they did it. The squeak has not gone away.

During the inspection they noted the oil boot was ripped (cheap part, I think about $20) plus 2 hours labor...they did the change. Squeak is still there. (also did front upper control arm, I wouldn't do this myself, either way).

Anyways, I'm sure they've looked at the AOS and didn't note that, could it really be as easy as a spark plug? My squeaking sounds 100% like the OP's, it only does it at low RPM/idle over 1,500 rpm it stops.

5CHN3LL

It COULD be a spark plug, but the fact that it goes away completely makes that seem less likely to me.

Macster

Why didn't you let the dealer techs diagnose the source of the noise?

I can tell you that rarely is the belt the source of any noise. But the belt should be changed if due on time or miles, regardless.

I listened to the clip again and after having heard something similar from my 996 Turbo a few months (or more) back my WAG would be the noise is an idler roller bearing.

But there have been enough cases of a loose plug that I couldn't dismiss that out of hand. That is none of my cars has had a plug go loose but other owners have, a few at any rate.

When were the plugs last changed? Are they due to be changed again?

If the idler roller bearing is the correct diagnosis you can confirm this by starting the cold engine without the belt. I assume though the noise is present at cold engine start? If so then this test at least lets you know something with the accessory drive is the source of the noise. If the noise is still present with the belt removed, then a loose plug, or possibly an exhaust leak is the source of the noise.

If you do the engine start with the belt removed be sure you take pics, make a drawing of the proper belt routing and note the belt's direction of rotation so you can afterwards install the belt back exactly the way it was installed before.

Added: Here's a clip of my Turbo making noise that proved to be from an idler roller bearing.

View My Video

I have two clips. This is the 2nd one. I mention this because the first clip I took from the very start of a cold engine start and the noise was not present. However, it didn't take very long, 15 to 30 seconds, before the noise appeared.

Frankie Cook

Here it is a couple years later and I had this exact same chirping noise on my 2001 911 996 and it happened to be the furthest rear drivers side spark plug had backed out and was loose. I changed all six plugs and coil packs as part of my 60k service along with the serpentine belt. Found this low mileage gem last fall when the original 74 year old owner traded it for a new 2016 911 because she was done using a manual transmission. My win!

Jrb37

I have experienced a similar sound when cold and idling. My guess is that the noise is less than 30 hz, doesn't seem RPM related, and gets louder when the AC is engaged. I have recently had the IMS, clutch, and water pump replaced recently - and the sound is still there.

I did the belt off experiment and did not notice the noise. Also did a stethoscope probe and couldn't find a piece close to the noise.

Coincidentally, the sound got significantly louder and more persistent just before the water pump went up. We were using the AC extensively, the water pump failed at a bad time, and the noise has me worried.

My current guess is that it is in the idler pulleys, or ???.

2004 C4S with 110,000 mi. Runs like a champ and uses no oil between 5000 mi changes. Oil has always been clean between changes.

5CHN3LL

Well, the good news is that it doesn't reproduce with the belt off. As long as this is accurate, you know that it's not an internal issue. Since you have had the water pump replaced, the list of suspects is now everything else driven off the belt: alternator, air conditioner, power steering pump, idler pulleys, belt tensioner pulley.

"Louder when the AC is engaged" seems to point to the air conditioner compressor, clutch, or bearing. When the AC is not on, the clutch makes the A/C compressor a very expensive idler pulley; when it's engaged, more stress is placed on the compressor pulley; a failing bearing seems like it would behave as you describe.

With the belt off, is there any play in the AC pulley? If it wiggles side-to-side, the bearing may be shot.

ZuffenZeus

Chanel, I squeak with my belt on or off. But I agree, no one should run around with their belt off.

Frankie Cook

JRB37 Spark plug check to identify for a loose plug! I wouldn't have thought it was that, and just knew for sure it was an exhaust part touching and metal on metal chirp or the idler pulley or water pump that was chirping. The fact that it wasn't missing or running rough and did it with noise only at idle or with little gas given, I don't know how it wasn't running like crap? Mine was literally almost backed out into the coil pack with maybe a quarter turn from being able to pull it out!

Just glad it didn't damage the threads so when I replaced it all was good. Both back plugs are a beast to get to and torque unless you remove the wheels and have it up in the air with some things removed. You can do it without doing that if you have small arms, hands like me and the right extensions, etc. I would give the plugs a check! I will do my own and not trust them to a shop cause that's how they ended up loose on the rear two spark plugs!

Good luck!