I seem to have the same if not similar problem in my newly rebuilt motor from Evergreen Engines in Spokane. However my rockers emit a squeaking noise sounding very much like a bad belt. Over any over I've tightened the rockers little by little (1/8 to 1/4 turn) over the past few months and this'll take care of it for about a week.... but then the squeak continues. I'm using the factory locknuts on the rocker studs and there's no apparent stud pulling. (If there's sufficient clearance I'm gonna try a straightedge along the tops of the studs next time). Sure is frustrating though. I'm used to once I fix something, by thunder, it stays fixed. Any thoughts on this?