I have a 95 Nissan pickup, 2wd, 4 cyl, short bed, 105,000 miles. I
bought the truck when it had 14,000 miles on it, and it has always
produced a slight knocking noise when cold at ~1500 rpm or so, no
load. No load means I push the throttle down just enough so that
engine is neither accelerating nor deccelerating the truck. This goes
away when warm. I had the dealer look at it, they found nothing wrong.
I have learned to ignore it.

Lately, the truck has developed a "knocking" noise when cold at ~2500
rpm and up, under load only. It's a moderately light knocking, sounds
a bit like piston slap but I can't be certain. It's too deep and heavy
to be an exhaust sheild rattle, if you have heard pistion slap before,
it sounds very much like that. I don't think it's a loose wrist pin
because that is not usually load or temperature dependant. It could be
a lifter, but would a lifter noise be load dependant? It completely
goes away after about 5-10 minutes of operation.

So, my questions are, is this something to worry about, is it normal
for this engine to do this at high mileage, and is it a sign that the
death of the engine is approaching? I might mention that the engine
does not burn any oil. I use 5-30 oil, but I had one oil change where
they put "high mileage" oil in the engine. I'm not sure what that is,
I have visions of them dumping a container of stp into the engine.