Yesterday on the way to work, I noticed a noise from the engine compartment that was new. Sounded like the timing chain rattling but not really. Only heard it at smooth running around 2200 rpm. Acceleration or deceleration and no noise. I was only blocks from work so I limped it in.
When I opened the hood, I saw a screw driver left carelessly on the valve cover and assumed it was rattling. Sunday was tinker with the M day. Problem solved.
Last night I got into the M to go home and it started fine with no noise with the possible exception of about 2 seconds of timing chain rattle. I let it warm a little and drove off only to hear the noise come back in the same manner as before. No rattling screw driver to blame this time. I parked the car and took my other car home. Spare cars come in handy when you drive a 14 y/o M3.
This morning I checked it and nothing in the way of noise until it warmed up a little, then there is a definite noise in the front of the engine. Plenty of oil in the engine, nothing mixed. I shut it down and came in here to write this note.
I guess I got lucky and am just before having the chain slip and destroy a head. Cars has @ 147k. No reason to believe a previous owner replaced the chain or tensioner and rails. When the valve cover was off the car a few months ago, everything looked OK and was tight, etc. No excess wear on the chain cog tips.
Any ideas would help.