Terrible squealing/grinding sound
 

I have a 2001 cummins, and in what seems to be the front of the motor, where all the pullys are, there is a squealing/grinding sound. I took it to a mechanic and he checked the pullys and said they all worked good. But is there a chance that even if you pull the belt of and spin the pully and it seems fine, that it may be worn out? This mechanic also said it might be a killer dowel pin or something wrong with the gears. If yall have any idea as to what this may be I would greatly appreciate any help.

I fought a squeal on my 99 for about a year changed everything from tensioner to WP, compressor pulley :argh:. Tried several brands of belts and finally a Goodyear gator back belt fixed it. They are available at NAPA and most of the parts store the sound never came back.
It started doing it at about 186000 miles if that helps.
How many miles on your truck?

Its cheap to try change the belt to a Goodyear gatorback!!

2ND that, Goodyear Gator Belt. from amazon. Mine stopped after the belt install 5 years later it does in once in a while on engine shut down. was about $18 from Amazon others wanted $35

It's got about 345,000. was the squeal in yours almost louder than the motor?

yes it was and very irritating. I was sure it was going to be a water pump or tensioner bearing. But after I changed them in a parking lot in Souix Falls lol i headed for GA listening to this squeal lol. The only other thing you might check is the ac compressor try to turn the front of the clutch its down low maybe easier from underneath.

I would also suggest spraying the serpentine belt down with a lubricant wd40 or like this see if the sound changes.
If it does, change the belt if not just wash the belt off with soap and water and move on.
If you use that belt dressing it is sticky and makes a mess but it works for a while.

Thanks for the help I'll give it a try. Hope it's nothing major haha.