skablaw

Hello all!

A few months ago my 2001 996 C4 made a high pitched squealing noise that started while driving in town. When I arrived home, I shut things down and thought I'd drop by my indie to check on it the next day, but it fired up with no noise and has been running quiet as a kitten until this morning.

I left for work and about 10 minutes into my drive, the squeal began so I pulled into a parking lot and took a quick video to capture the sound, which I've posted on YouTube at http://youtu.be/zJMefjFx_y4
. Things I've read here suggest it may be a failing AOS, but I have no oil pressure issues and no smoke eminating from the exhaust - symptoms that seem to accompany that particular issue. Any thoughts would be greatly appreciated. Thanks so much!

-Steve

Macster

If not an AOS and the noise may not be due to a failing AOS, then another possible cause is a dry or dragging serpentine belt idler roller/tensioner roller bearing, or a going bad water pump (or other accessory) or a tensioner that has lost some of its tension.

One trick is if you know the noise is present at a particular time, is to remove the belt -- note its routing and direction of rotation carefully! -- and then start the engine and let it run only long enough to confirm the noise is still present or not present.

Obviously you can't remove the belt from a hot engine and then drive the car down the road for 10 minutes until the noise appears. Nore can you remove the belt from a cold engine and start the engine and let the engine idle 10 minutes until the noise appears.

Anyhow, if you can do the above test without risking the engine, and if the noise is still present with the belt removed, then AOS becomes suspect #1.

If the noise is not present something related to the serpentine belt/accessory drive is suspect.

Sincerely,

Macster.

San Rensho

Linky no worky. To rule out the AOS, with the car running, remove the oil cap and put your hand over the opening. You should feel just the slightest vacuum, almost imperceptible. If you have major vacuum, then likely its the AOS.

Pac996

Change the belt. In my old engine I would get the squak racket out of the belt at start up like it was starter noise. Just the belt being stiff/glazed and not taking to quick increases in rpms like going from 0-1,000 rpm in a split second.After replacing mine I never got another squak out of it. I could of sworn it was a bearing but I guess the bell shape of the pulleys kind of mask the real culprit and amplify the noise.

Oh yah, the belt is a quick cheap change you probably are due to do anyway so start there.

logray

Could be a pulley, could be the AOS. How is the coolant level.

+1 to run the car very very briefly without the belt on.

skablaw

I posted the video on YouTube at http://youtu.be/zJMefjFx_y4
- hopefully that will work for everyone in listening to the noise. I will see about testing whether or not it is a pulley. My suspicion is perhaps not because when I shut it down there is a sound like a whistling as that squeal dies down, but I'm no expert so that may just be the sound of the pulley as rotation slows.

Gonzo911

Cooling fan?

RPMulli

Dude, that sounds like a running power steering pump with no fluid

logray

Wow, after listening, sounds much more serious.

Yes could be something like p/s pump w/o fluid.

Should be easy enough to pinpoint if you can duplicate the problem, just remove the airbox and either remove the belt and run it briefly or with something that noisy you might be able to just hear it and see it easily.

skablaw

I've made my way to my next obligation for the day. I just saw the replies on my phone coming into the building so when I'm done here I'll check on the power steering pump. I should just be able to look and see if the reservoir is dry, right?

If it adds anything to the analysis, the sound didn't start fora few minutes into the drive, but once underway it was constant except when I was on throttle. No matter the engine speed, when my foot was off the pedal or just "maintaining" the sound kicked in, but putting the right foot down silenced things. Too bad I can't just accelerate indefinitely!

RPMulli

+1, just check the p/s fluid level with the dipstick. Remove the airbox and take off the belt after the engine is hot or whenever the sound occurs. It is hard to tell where the noise is coming from in the video and whether or not the camera is distorting the noise. Is does sound like crap... the noise just reminded me when I started the car without p/s fluid in the reservoir. How's the weather out there? I just moved from Bellevue last year, I spent 8 years in Nebraska. Hopefully you can pinpoint the sound and cross your fingers that it isn't something internal.

Is your a/c on or off when this happens? I know the weather has been warm out there.

BTW: You better post some pics of your car!!!!

Mark I

Sounds more rotational than the pressure release sound associated with an AOS. Forced to a guess, I'd say alternator bearing or tensioner. +1 on checking with the belt off, check everything that turns by hand if the noise is gone with the belt off. Keep us posted. GL with diag. & fix.

sjfehr

Check the P/S level first, it's easy to do and either confirm or rule it out.

The sound is slightly different than when my AOS failed, but your symptoms are identical to when my AOS failed- the sound didn't start immediately & lessened with acceleration, but was LOUD and otherwise sounded dead-on like the sqeal of a slipping belt. With the engine running and squealing, try to remove the oil fill cap- if it's extremely hard to remove but the sound stops immediately after you remove it, that's your confirmation it's the AOS. (If you find it impossible to remove while the car is running, that's a pretty good indication, too.) Word of warning: immediately put the cap back on, or the additional airflow is apt to suck a lot of oil into your intake manifold through the failed AOS. Which will remove all doubt, sure, but kinda makes a mess and a lot of embarrassing smoke.

Pac996

wow thats some angry chipmunks

skablaw

It's the AOS alright. I just got to the gym and The shrieking started up a few minutes ago. I hopped out and tried the oil filler cap test. Sure enough it gave a good fight before popping off with a swoosh like a city bus releasing the air brake and the squeal went away immediately.

Thanks, everyone, for the advice! My next question is how long can I drive around like this? She's my only ride so if it isn't safe I'll have to take her to the shop, but if I'm okay for a few days I might try to order parts and do it myself. I can get it up on jack stands and lower the engine a bit, which is what it looks like it will take. A lot of posts say it isn't that hard, but some are saying their mechanic charges for 8 hours of labor! What do you guys think?