92 Lesabre low idle rattling knock with AC on

Hello Guys. :banghead: This is for the most experienced members. My 92 Lesabre 3.8 v6 has a loud rattling knocking sound at low idle with AC on. The AC has been checked by the pros. The AC comp is new. The following has been replaced, harmonic balancer, AC comp, Alternator, water pump, Idler tensioner, Timing chain and gears, oil pump pressure relief valve and spring, serpentine belt. The noise appeared about a month after having the AC pump rebuilt and the system charged. Prior to this it had timing gears and chain replaced. The noise started after a month of really hot weather. The first suspect was the water pump as the sound seems central on the front of the engine. Not it :disappoin . Then the alternator, not it :disappoin . Then the harmonic balancer, not it. :disappoin Then the belt tensioner and bearing, not it :disappoin . When using a stethoscope the noise is loudest on the casting where the oil filter spins on :banghead: . Everywhere else is quiet or the noise is faint.This led to the oil pressure relief valve, not it :disappoin . Does anyone know if the oil pump gears can rattle and knock at low idle. It only happens when the AC in on. I goes away with an increase of 100 rpm. The AC pump is quiet with a stethoscope, as is the steering pump. At present the timing cover is off to check the timing chain to see if something went wrong there. Everything looks good. I'm planning replacing the oil pump gears, maybe they rattle, but first I'll remove the oil pan and look for metal fillings or metal in the oil. I'm pulling my hair out on this one. Sounds loud enough to be crank related but the oil pressure is really good. Anyone experience anything like this? It is at idle in park or drive AC on. Touch the throttle with slight pressure and it's gone. Turn off the AC and it's gone. But the AC is good. I first suspected the AC clutch but the pros say AC clutchs don't make that noise.This engine has a balance shaft above the cam, not sure of it's purpose. Could that make noise? Either more rpm or more oil pressure makes it go away. I think it may be something simple that I have overlooked and will feel dumb when I find it. Please help! The top of my head is starting to look like Homer Simpson's. I have to find the noise before I loose those last three hairs! I'm too stubborn and interested to give up. OK guys I know you're all thinking hard on this one, I can smell the wood burning already! Call me Bacon. Thanks :banghead:

It's me again. I just thought I would update those of you that have read my first posting. I still have the timing cover off. I ordered new oil pump gears from GM. I got those today. When cleaning the oil pump cover I discovered the gears have been hitting the cover in two spots. I then rubbed the cover on crocus cloth on a flat surface then checked to see where it is contacting the paper. Contact is only around the edges. The center is worn away by the gears. A new cover has been ordered.
The oil pan is off now. Really clean in there. Oil had nothing in it that shouldn't be there. Now the balance shaft I mentioned. It runs off a gear on the end of the camshaft, behind the the timing gear. I cleaned everything and when I used compressed air to blow the bits of loose gasket off the engine I thought I saw the balance shaft gear move. I placed my thumb on the balance gear and it moves. If I move it back and forth fast it knocks! My question now is, should there be that much play in these gears? My books don't help. Now I will order those gears new. Has anyone removed these gears before? I know they line up just like the timing gears. Each balance gear is held on by a single bolt. Are they left hand or right hand thread? Since it's a gear driven apparatus I assume one is left and the other a right. I also assume an impact gun is the only way to loosen the bolts.
While I have the pan off I'll check the front main bearing clearance. I've heard that 92-94 3.8 buicks have a problem with too much clearance on the front main. Does anyone know if the front main bearing can be replaced from under the car? I've never tried that. I suppose if it's too loose I can spin it out of there and then spin a new one in. Anyone got anything to add? :banghead: I lost another hair today. Only two left.