I have an '05 T&C with 173k. When I would turn on AC Compressor and it'd kick in I'd hear a rumbling sound in the cabin. I replaced the clutch bearing and the sound persisted. The noise only occurred when the AC Compressor came on. Therefore I replaced the AC compressor and wouldn't you know it.....the noise did not go away and it still makes a rumbling sound only when the AC Compressor kicks in. What else could be causing this.. I have never had need to replace alternator and is putting out proper voltage, and close listening to it yields no noise. I have looked to make sure nothing is in the way of the compressor that could be touching it, or any other thing that could be in the way, rubbing, touching in the drive line etc..... Ideas??

 

I have the same trouble and replaced the belt tensioner as it seemed to eliminate the noise if I took tension off belt. Thought it was tensioner pulley. But it wasn't. I am thinking a/c clutch but your post makes me skepticle

 

Check this site Litens OAD Decoupler Pulleys
Alternator has a decoupler or over run pulley that starts to go bad. It is easy to exchange if you have the tool. I bought a tool on ebay and a pulley for $50 total.
As the pulley continues to fail, it will start to constantly make noise. Mine sounded like a jet engine shutting down when I turned the van off as the alternator came to a stop.

 

Alternator Decoupler Pulley, where can I buy? Good brand Serpentine belt?
Another forum to check out as well

 

I replaced the alternator with a new one. i thought about just doing the decoupler pulley, but for an extra $100 i got a new 160 amp alternator. the original alt had 100k+ miles and could potentially quite at anytime, so I went with a replacement.

That was the noise. pretty easy to do probably about an hour.

thanks for the input.

now ive got rust to repair, Im thinking about buying a wire welder and welding in new panels.