Hi All,
Diesels are very noisy in the air intake, are you using an Isuzu (diesel) air box set-up, if not I believe Chevy V8 diesels have an air silencer in there air system, mite be worth a trip to the wreckers.
Many years ago I had a Toyota diesel in a Mity van, the air cleaner made more noise than the exhaust, fitted a Nissan silencer and that knocked the noise back a lot,

Peter H

1994 BigHorn Lotus (Trooper)
3.2 DOHC