Because I fit a lot of electronics to new Hilux's I've noticed as with my own Lux a loud vibration from behind the dash (behind glovebox).
This usually happens under load and sounds very metallic in nature. Because my car is sound proofed, it is extremely loud for me so I just had to get rid of it (also my sub sets it off big time).
It was easy to find and fix as you just open the glovebox and pull it up and it will come out. Behind it you should see a computer box that's mounted vertical. I removed the wiring and clips but it could be done in position if you were lazy but its only 4 nuts/bolts (do not turn or leave they keys in the ignition while doing this). I then applied sound deadening to both sides of the housing. It fixed it a treat!!!!