As mentioned above, a good, free and easy test would be to look at the motor mounts. At least determine if there seems to be a problem there or not:
1) Open truck hood, Start truck, look at top of engine between hood and lower windshield
2) Hold foot firmly on the brake pedal, put truck into D (keep an eye on engine).
3) Give the accelerator some 'gas' (foot still firm on brake), and see if the engine rocks more than, say, and inch.
4) Then try the same test but this time putting the transmission in Reverse.
5) Keep foot firmly on brake pedal. Don't let the truck lurch or move. Make sure no people are around truck.
If a motor mount is 'bad' or 'failed' an engine will generally lift UP quite a ways.
You also might be hearing nasty harmonics brought on by air rushing through the air tube on it's way to the engine. Are you running a cold air kit or non stock air system?