Noise from alternator area - 1998 4.0 SOHC

[bryansr]

There's a rattling noise coming from somewhere around the alternator on my 98 only when the AC is turned on. I thought it was the alternator so it was replaced last weekend but the noise is still there. The AC compressor is on the opposite side so it can't be that, and I'm hoping it's not the timing chain guides but there's nothing else in that area. It only happens when the AC is turned on and never when it's off. And the noise is not constant the entire time the AC is on.

Any suggestions on what it might be?

Thanks,
Bryan

 

[swshawaii]

Maybe?
Signs of Belt Tensioner Failure
1998 FORD EXPLORER 4.0L V6 SOHC Belt Tensioner | RockAuto

Also check ALL other pulleys, especially the idler pulley.
1998 FORD EXPLORER 4.0L V6 SOHC Idler Pulley | RockAuto

 

[J_C]

Happening hot, cold, or when?

One thing to try is just take the belt off and run it. If the noise is gone it's probably something belt driven. Granted, you can't run long without the alternator or water pump.

 

[bryansr]

Yep, I was wondering if it might be the belt tensioner since it's right below the alternator.

Haven't correlated it to engine temp. It only happens when the AC is turned on, so I'm guessing it won't make the noise with the belt removed but I might try it.

 

[swshawaii]

Inspect the tensioner with the engine running before removing the belt.