Engine experts, I need some help.

[Shifter]

In the spring when we first put the engine in and started it, it made a "load specific" noise. Kinda like a knocking sound, at least that's how I'd describe it. The noise is non-existant at idle, and it does not do it revving it. You can stand over the engine and listen, and rev it from idle to 6,000 and all you hear is exhaust and the sewing machine sound from the roller rockers, it sounds good and strong. It only does it when the engine is under heavy load-lower rpms(rolling in 4th gear at about 2500 rpm's and rolling into the throttle increasing as you push on the throttle.) the noise goes away after about 4,000 rpms. Since spring I figured it would get worse and show itself. If anything I think it has gotten less. However it is still there. Oil pressure is good(75psi warm, driving), I now have about 800 miles on it and a day at the track(12.40's at 115) and a bunch of back road pulls. Its weird and has most of the people around here puzzled.
Please give some advice.
Thanks, Lou


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'89 LX, Carbed 331, AFR 185's, Tremec, 8.8 with moser guts and 4.10's....
'90 GT (Wife's car) Custom Bright Red, mach one hood, Drag Lite's, Mostly stock with an AOD.
Daily driver-gets about 26mpg.