Truck making a squealing noise

When I let off the gas, my truck makes a squealing noise. It stared when I put my new muffler on. Can anyone help me figure it out?

 

Just had my truck at the dealer today for same issue. They can't figure it out. Only thing that I had done 2 months ago was replace water pump and timing belt which they checked today and everything was fine. Squealing starts when letting up off the accelerator but is not consistent.

Any thoughts appreciated.

 

Try checking your exhaust brackets, sometimes if they're worn/bent, or not in the exact same position, you'll get a metallic squealing noise from your undercarriage, especially if you've had the exhaust apart, it happened to my '01 and '04's prior to replacing the whole system.

 

Dcmh, look into tightening your alternator tensioner...

 

Thanks.. figured it out last year lol

 

So what was it?