The car runs awesome, smooth, takes off real quick, shifts nice etc. But when it warms up, one of the lifters i think don't have oil in them, so it starts tapping and literally making a knocking. This only happens when i run the car at higher rpm's, 3000, or 3500. If i let the car sit and idle, the sound will slowly go away. Could it be that sludge is clogging it or what is going on? There is no noise at all when it is cold. Not even the cold lifter tick. It did it with 15w 40, then i change the oil pan gasket, cleaned the oil pan, and refilled it with 10w 30 with GM EOS. I looked at the camshaft and it was glossy and smooth. What should i do? The noise isn't a tick, its a tap, not always, onyl after i drive the car harder than usual then it goes away.

Sounds like the oil is getting air trapped in it when operating at slightly higher engine speeds and causing air to get pushed into a lifter causing the noise. The fact that the noise goes away after driving normally for awhile confirms that.

It is some what characteristic of the early HT4100's for that to happen. This can occur because of the design of the oil pump pressure relief valve port in the oil pump. It vents the pressure relief oil directly back to the sump external to the pump which could cause air entrainment because of the oil spraying out onto the surface of the oil in the pan.

If you were to look at the oil pump for the later model HT's there is a small shield on the side of the pump that directs the oil pressure relief oil flow downward below the surface of the oil to prevent the aeration. If you have some engines to look at find an 88 or 89 model 4.5 and see if the oil pump has a shield on the exterior to cover the bypass relief port. Use that on your HT4100 pump.

If you want to fix it and/or prove whether this is the problem or not you could drop the pan again the unbolt the oil pump. Look at the pump. There is a hole in the side of it that is the pressure relief bypass valve exhaust. Oil comes spraying out of the hole when the pressure relief valve is in operation. Make a shield out of a piece of 3/4 steel tubing to cover the hole and direct the flow downward toward the oil pickup. Just a two inch piece of 3/4 tubing, split in half with a mounting tab to hole it in place. Close off the upper end of the tube so all the flow will go downward and the oil aeration at higher speeds will be dramatically reduced. Or....just get a gerotor oil pump from a later model 4.9.......