My problem is very odd and elusive. On Friday I started to hear a noise that sounded like a person patting himslf on the shirt. I have traced it with a stethoscope to the bottom of the engine. It is most audible once warmed up. It reminds me of spark knock, but it is not. I have taken it down to 10* timing at 93 octane with no avail. Next I thought of a loose lifter. Set the valve lash again, same problem. Next I made sure that nothing on the engine was hitting the fender etc. That checked out. Re torqued the header bolts, same problem/noise. Check spark plugs, looks good, just hot.

I have been monitoring all of my sensor readouts, all reads normal. No oil or coolant is lost and oil pressure is fine. Could it be a timing chain? I did notice a few hiccups when adjusting the timing. it would go up two degrees for a 1/2 second then regular. There is no shake at all when it is idling or reving or driving as a cylinder not firing might present.

I next thought it could be a loose bolt on the tranny/flywheel/clutch/bellhousing. Well one of the top tranny to bell housing bolts was finger tight, the other top one was 1/2 way out. The pressure plate/disc was a little misaligned, but all of the clutch and flywheel bolts were correctly torqued. So I started the engine with nothing after the flywheel. Noise still exists.

Look in my sig. for additional car info. Any suggestions on where to go from here would be appreciated.

 

Maybe try pulling your belt(s) off after warming it up and see if the noise is being caused by misalignment and the belt riding up the edge of an accessory then slapping down. It may seem to come from inside if the snap is bad enough to make it to the crank.
Just a thought after everything else fails.
Jp