I, too, have a '95 trooper with noise. Mine is a 95 LS w/ a five speed. The engine is the sohc 3.2. The noise is from the cam followers and rocker arms , which open and shut the valves. Some call these lifters. They clog and flatten out over time. Isuzu says it's due to infrequent oil changes. My experience has been different in that my oil has been changed faithfully in excess of the manufacturer's specs for the life of the vehicle. I've been running amsoil synthetic since 50k and now have 125k. I have replaced a couple of followers already. I'm going to replace the remainder of the cam followers at the end of the month. I should have done them all at once. Some strategies I tried to put off the lifter replacement: Switch to a light weight synthetic -- 5w30 or 0w30. Heavy oil may make the noise go away temporarily, but it exacerbates the problem over time. The root cause seems to be oil passages that are too small -- sort of like clogged arteries. I have also heard or read that the cam lobes may have been manufactured with a less than ideal alloy, which causes a reaction over time that results in the followers flattening out and thus sounding like you just bought a deisel. I also used various engine cleaners like rizlone, BK products, amsoil's own cleaner. They were temporary, at best. Once the knock is with you, it's not going away until the lifters are changed. When I replace the remaining followers in May, I'll be interested to see the state of the two new followers I put in about a year ago -- my question being, does replacing the them fix the problem for good, or for how long?
Good luck. Let me know what you do. I'm stuck with my trooper for a while because I just bought a new(er)honda. Nothing else has given me trouble on the trooper, so it's a small price to pay for such a faithful goat.
BigFish