First of all, I am new to the forum and thank you all for the ad. I always seem to find the best answers to tech problems on the forums, well, at least the most options! I have just purchased a 2005 Chevrolet Tahoe Z71 4x4 for my daughter. Has 200k miles and has an engine tap that sounds like a collapsed lifter. Oil pressure was about 5 psi at idle. SO.. TOTAL engine rebuild. I mean TOTAL. found some bad cam bearings but the cam/lifters and mains looked pretty good. Replaced EVERYTHING regardless of its condition. Re-installed motor and engine runs beautiful..Great oil pressure, and then....once she's warm, the tap returns. Everything still running great, oil pressure good, smooth idle, but the tap sounds like its coming from the bottom side of the motor. In the oil pan/bell housing area. 5 of the best mechanics I know have looked at this and no one can narrow it down. flex plate is good, and I have a hard time believing its interior motor being the fact the noise is the exact same before and after complete rebuild. Anyone have ANY suggestions?? Losing my mind