Another thing that can help determine exactly where the noise is coming from is a 2-3 foot long piece of garden hose.
Holding one end to the ear and moving the other end around the engine can rapidly narrow down the source of the noise.
If it's coming from the rocker arm covers, it's caused by loose valve adjustments so tighten them up just a bit.
Don't over do it. With the piston at TDC they should spin freely when the engine is still cool, with just finger pressure.