Don Magee

My 1995 993 is making an odd noise. Noises are hard to put into words, but I'll try. When the car is resting at idle, or going slow in a parking garage, I hear a sound coming from the engine bay that is best described as like a few pebbles being rattled in a tin can. The car is stock back there. It sounds vaguely like a car with a light weight fly wheel, but it sounds to my old, deaf ears as if it is coming from the engine fan/ alternator. I had an alternator go out about a year ago, and the replacement was defective(rebuilt) so another one was put in. When doing that, the alternator shift was frozen solid to the hub assembly , so the hub was replaced. I also had the fan replaced, because one of the blades had a hairline crack. When I got it back, it sounded a tad different. Not bad, just slightly different. New fan, belts hub and alternator, so I was not surprised that it might sound different. Now, a year or so later, this sound develops from the same area? Any ideas? It is just sort of a rattle. Cant hear at speed, but I suspect it is just drowned out. The fan does not vibrate or appear out of balance. Belts appear tight and are not wobbly.

BobbyT

You may want to inspect the fan and its shroud for any evidence of contact. Also you can check the clearance between the fan blade tips and the shroud with a feeler gauge, to get a better idea of potential contact.

Otherwise, could it be something broken loose in a muffler? Loose muffler strap? A broken fender brace?

mr_bock

+1

Leander

Yup - sounds like the alternator fan.

AOW162435

Definitely check for fan/shroud interferance at the bottom. Belts that are too tight will prematurely stress the fan hub bearing as well as the alternator bearings.

Also check the silly belt sensor wheel for damage.




Andreas

kjr914

Get a mechanics stethoscope and poke around (not near the belts). If fan is hitting the housing, you should be able to see some evidence on the bottom (usually) of the shroud between the fan blades. Check clearance with feeler gauge mentioned above, or even a piece of paper or (thicker) construction paper to see if it catches and hangs on the tips.

One other way....
start car and ensure you hear the noise.
disconnect/remove the AC belt and start the car again. Noise or no noise?
Then disconnect/remove the alternator belt, but put spacer & nut back on to keep fan running, start car. Noise or no noise?
Then disconnect/remove fan belt, replace spacers and nuts (to keep stuff from flying off...), start car. Noise or no noise?
If its the fan/alternator/belts, this should locate which it is.

Don Magee

Thanks much for all of the help. I will poke around this weekend and report back.

pp000830

The AC clutch can make noises like this even when nothing requires servicing. The sound should go away when the AC compressor is engaged if this is the source.

jenskleis

Are you sure that the noise is coming from the engine bay or could it be from the rear of the car?

I had a rattle at idle, which turned out to be one of the screws that hold the inner rear wheel housing cover in place. It can tap against the inside of the rear wing.

Wheel Dynamics

And here I was all happy thinking that I would click on this link and see a cool video like this one.....

Oh well, it's Friday and my oldest boy is testing for his belt so I'm happy.

But for those who thought the same thing I did, here's to you!

Don Magee

The video was great. I'd thought about trying to record my imitation of the sound and posting it, sort of like they did on the radio show Car Talk, but didn't want to embarrass myself further.
Here is the update: the fan bearing has failed.

skl2

I was thinking this exact same thing. Happened on both my 993s.

Don Magee

I didn't think about the wheel well, but I did think that it might be a loose exhaust bracket. But upon closer inspection, it was clearly coming from the fan/alternator area.

NC TRACKRAT

"Here is the update: the fan bearing has failed."
If you don't already have one, purchase a "Klikit" belt tension gauge to avoid excess strain on the bearing.

bcameron59

Krikit gauge also know as Gates 91107 (or Krikit 2, Gates 91132), easy to find on Amazon, for example:

https://www.amazon.com/Gates-91132-B.../dp/B000CRDLZM

No affiliation