I seem to remember people referring to an interference problem between the connecting rods and camshaft lobes if there's a slight out-of-time problem on the cam. I've never experienced it myself, but I've heard it referred to several times since I've been a member of this site. Now that you have the oil pan off, start looking for a connecting rod/cam lobe contact point when you get into the neighborhood of the position whete the noise happens. Also, if a part of a tooth on that fiber timing gear has broken off, it could have jammed into the gullet of the tooth and created a tight spot when that set of teeth mesh. Definitely take the timing cover off and inspect the gears!
Jerry
