I just bought a 95 powerstroke dully f550 w/25 k on it. I believe it has a few mods....not sure. After about 900 miles i noticed a loud sound when the turbo kicks in it sounds like wind rushing in the engine somewhere, almost like it's pounding against the firewall. I've also noticed on my turbo gauge that it used to peak out at about 18lbs of boost now seems to only want to go to 10lbs. The engine seems to be lacking some acceleration along with this. Any ideas?

 

To me, it sounds like you've got an exhaust leak upstream from the turbo. That would explain the noise you're hearing, and also why there would be a drop in boost. I'd check there.