Grinding noise under the hood
 

Hi,
I'd like to get your advice regarding the grinding noise my 2001 Caravan makes under the hood. It is something that has been "running" for a few months but since I'm going away this week I'd like to make sure this is something I can fix or is not going to stop the vehicle. The noise itself is like a failing ball bearing or metal grinding. If the car is parked in "P" it runs OK (well let's say so). As soon as I step on a brake pedal and shift to "D" I can start hearing this noise. The same happens when the car is parked but the A/C in turned on. I looked arround the compressor and is OK. It looks like the noise is coming from way above more less where the belt tensioner / alternator is - near the ECG valve. I'm puzzled thinking that it may be a water or power stearing pump. Is it possible that the alternator makes that sound. It is the original unit and my car has already 190k clicks. I'm prepeared to replace the alternator today but I wondered if you have any other suggestion. This is not releated to suspension, CV or any other part down there. I appreaciate your comments and suggestions.
Thanks

it is nearly impossible to guess at a noise issue without hearing the noise.

I guess it would be a drive belt related problem like you are thinking or transmission issue or timing chain or ??????but without actually inspecting and hearing it in person that would be purely speculative

Transmission - no. It's 100% on the other (serpentine belt) side. Timing chain? Possible. Drive belt? Most likely. The only question is why is this sound "generated" when the vehicle is in "D" or with A/C on? When it's parked it seems to be running fine.

think about this from the other perspective, how would you be able to state what the noise is and were it's coming from if you can't hear/feel it?

when the engine is in drive there's load put on the engine which changes effects on moving parts. it could be about anything but again without being able to see/feel/hearing the problem it's purely guessing what it could be.

diagnosis needs to be done using a process of elimination. take off the belt and see if the noise is still there, if so it's not anything with the belt system. if it's gone then pursue the moving components related to that system.

I agree with Sapporo in that it needs to be a matter of elimination. Our van had 152k on it this spring when it started a similar grinding sound. I figured that since I wanted to get at least another year or more out of the van, the water pump was the most likely to fail and strand us somewhere so that was replaced. It didn't fix the issue but I had some peace of mind knowing that at least one component wasn't going to fail on us unexpectedly.
I figure at this point, it's either the idler, power steering pump or AC clutch which I believe are the only other things that rotate with the engine.

OK - problem solved. It was the alternator. I replaced it last weekend and when I pulled it out I checked the clutch pulley and it appeared to be somehow loose. The one on the new alternator I could not move at all. Also the ball bearings were a lot smoother on new unit. This was the original unit and as of yesterday I have 196k after returning from Canada.

that's awesome. and the best part is you reported back so we know the problem and solution.