I have a 2001 Caravan, 3.3L, FWD, 194K+ miles. For the last 100K or so, there has been an engine noise that is baffling me. The noise is a cross between a rattle and a whine and is audable over engine noise at an idle but not at highway speeds, probably due to engine noise plus road noise. The real kicker is when I turn the engine off. For about 3 seconds after the engine stops, the sound winds down from the normal higher pitched idle whine to a lower crackling sounds right before it stops.

The replacement of my A/C compressor and serpentine idler bearing, about 60K ago, did not change this whine.

I can not think of anything else that continues to rotate after the engine stops.

Anyone have this problem or have any cool ideas??

Oh yeah, and is there anything in the transmission that could be doing this? I haven't thought so because it has been working perfectly.

Also own:
2004 DODGE DAKOTA QUAD, 4.7L, 4X2, STOCK

 

Have you checked the alternator clutch pulley?

 

Welcome to DF
Try isolating the noise by removing the fan belt. If the noise is gone, then the problem is belt driven. If the noise is still there. Then you need to look further.

 

I didn't know there was a clutch on the alternator but I will check. Wait...

Is this a joke, like the muffler bearings and the blinker fluid? I was a engineer equipment Mechanic in the USMC, but there might be something new on the alternator...

I will check to see if there is a clutch on the alternator like there is on the A/C compressor, but I wouldn't think so. I could make sense though. That would be better for the battery and the alternator.

Will get back...

 

I will attempt that along with the above post. Good idea. Can't run too long cause I think the water pump is attached...

 

Its a joke!

 

Actually, I don't think it is a joke.

It is called a Isolator Decoupler Pulley and it was designed into the caravan to reduce NOISE...

Check this out: http://www.decouplerpulley.com/files/RotoRxbrochure.pdf

I can't find a way to buy and replace just the pulley though.

 

I didn't know it was called a decoupler pulley. Part department always gives a price on the alternator.

 

It does sound like a joke but it's not. It is basically a one way bearing with a buffer spring. The idea is when the engine suddenly slows the alternator can freewheel until is slows to the engine speed. It reduces the stress on the belt and belt driven accessories. Earlier models had problems with throwing belts.

When you stop the engine the alternator continues to turn and a bad clutch bearing can make noise.

 

It looks like a normal pulley except it sticks out a bit in the front. You can replace just the pulley but the problem is you need a special tool and it can be hard to find the correct pulley. Most cheap aftremarket units are just a one way bearing. Better than a solid pulley though. The special tool is basically a large allen to grab the inside of the outer pulley and it has a hole in it where a socket like tool grabs on to the alternator shaft. The shaft threads right into the inner pulley.