Crazy Loud Turbo Whistle!

New to the forum.... My son bought a Pete with a C-15 6nz. Pulling a grain wagon. He has been complaining about a super loud whistle coming from the turbo. It starts around 15 psi boost and is obnoxiously loud thru about 20 to 25 psi boost. (I've driven the truck and can vouch for it) We've had it in a 2 reputable diesel shops and they have gone over it with a fine tooth comb looking for air leaks. We finally had the exhaust totally resealed to try and make sure. Still no luck. My son has read online about maybe sticking a silencer ring before the turbo??? I guess it is done on pickups sometimes??? We are out of ideas and getting a little frustrated. Any thoughts?

Thanks!

 

I know their will be noise.... But this is CRAZY Loud! It is incredibly piercing. Loud enough that you would need ear plugs. If the noise was at a point in the boost that it wasn't their very long, a guy could handle it. But it is right in that 15 - 20 psi range and that is where it sits a lot going down the road.

 

Yes I have.