I have a 1993 Mitsubishi 3000gt manual with 121k miles and when I’m driving theirs a loud knocking sound when I gas the pedal it goes away and once I let go it comes back and the faster I go the louder it is.
If it comes from the engine, you probably need to to fix the lifters which does not worth it. Either get rid of it or keep driving it until the wheels fall off . To help the situation, you may change the oil more frequently and add oil additives (Lucas has one).
Lifters shouldn't be too hard to do. Just pull off the rocker covers and check. The rear bank is a bit of a hassle as you have to remove the plenum but all is not lost.
Definitely check the valve train, but IMHO if it is knocking, and not tapping/clattering, this could be deeper in the engine.
Rod bearing or main bearing.
