engine rattle

I have an '88 b2200 that has a knock/rattle. Ive been driving it with this rattle for 6 months and about 8,000 miles and hasn't gotten better nor worse. Two of my local shops told me it was a loose rocker arm so I switched the hla's to the b2000 system since I heard that this system was much better and cheaper to maintain, but the knock is still exactly the same. The noise comes the most on light acceleration and if I'm on the freeway when I let of the gas just a tiny bit. The speed of the knock does sound to be at the speed of the rocker arm however.

The noise is just plain annoying.
Any ideas??

think that year of turck has a mechanical fuel pump?

Hmm, I'm interested in this as well, I have a knock I haven't been able to track down that I'm positive isn't the HLAs.

if its only at certain RPM's then it sounds like rod knock. could be a bent rod. also, try using higher octane to rule out detonation.
to see what cylinder it is just remove the plug wires one by one while the truck is running. if you pull wire 2 and the noise stops then its that cylinder.

I also thought it could be the fuel pump(mechanical). I pulled it off this morning and saw it had about 1/4 in of play going in, I bought a new one for $26 and compared and found that there is no play in the new one so i just replaced it.....noise is still there. It made perfect sense since it runs similar to a rocker arm

If it were a rod knock wouldn't it get worse over time? I pulled the wires off one at a time and found cylinder 1&2 to make the knock just a tiny bit quieter, just a bit

My dad isn't really mechanically inclined but told me once he owned a Ford Tempo that would make a similar noise and he would just change the header gasket every 10k miles and it would go away. I decided it was worth a shot so i pulled off the heat shield on the cat that bolts to the header and saw a half inch crack on the cat right under the mating section. Is it possible that this makes a knock? Also since the noise is most obvious when driving I'm also thinking about something related to flywheel since its closer to the cab and once it came loose due to previous owner not using proper torque.
It's just loud to where I can't pin point the exact area where it knocks

Wrist pin, if it was a rod, after 8000 miles it would have gotten worse. Hows your oil pressure ? it should be 58 lbs. @ 2500/3000 RPMs with the engine at running temp.

At certain rpm and certain throttle positions it could be an exhaust leak, (or piston slap or... or... lol) any chance you can grab us a recording?
Someone may have heard the same thing and have the answer you're after

Just to add to this, I did track down my funny noise, and it was a slight exhaust leak where the tubes for the PAIR system were brazed together. It would come and go with changes in engine load. Fixed that up and all I hear are the HLAs now

Cool

I checked out all my tubes and header the other day and made the best mistake ive made with this truck, I left the distributor vacuum line disconnected and the noise went away. I just hooked it back up nd the noise comes back. Could I have the vacuum line coming from the wrong part of the intake or a bad distributor?