When the car is warm I get a knock coming from the bottom end/back of engine. But it only does it at idle when the idle stumbles or surges(another problem). Only does it every 5 to 10 seconds. Seems to be running good. Oil pressure is good and compression check is good. Could this be a rod bearing? Is there anything in the bellhousing related to the clutch that could cause this? I have a feeling this going to require pulling the engine to solve.