On one of my old motors, I was at the track and it started making a terrible "clack! clack! clack!" I thought Id lost a valve or spun a bearing. So I got it home and had torn the intake off, all the accessories off, exhaust off all the way to the muffler, untill it was just a bare long block.
then I decided to pull the cam cover off...... and it had just dropped one of the intake rockers.... and i was like "wow... really?"
took everything off for nothing and had to put it all back together