On my truck I get alot of the diesel noise. Its mostly caused by a exhaust header gasket leak. Its worse when cold, untill things start warming up and expanding, but it never goes away completely. For me its not worth braving the rusted manifold bolts to change the gasket. I spent a lot of time trying to trace the noise, I probably checked and adjusted the valves two dozen times thinking it was valve noise.
But, both of those things are worth checking into before you do more drastic repairs.

-1989 4x4 22re(pretty good in the mud)
- custom steel flat bed-oneside of exhaust system, and air box intake off cobra.(doesnt quite have the v8 rumble)AFM off '82 Supra.
-Destination M/T 31"-KYB monomax shocks-"add a leaf"