Just finished building 540 cu in with 440-1 heads cr 15-1 Comp Roller Camshaft running a toilet bowl on alcohol. When engine temp gets up around 170 degrees there is a clank sound, like you take a wrench & hit the tool box sound, but it's not from bearings or valve train sound, sounds more like a convertor bolt or starter engaging, coming out passenger side header. The header gasket does not appear to be leaking can not find any leaks in header, we pulled the header off the car to check it, flywheel torque converter bolts are not loose or hitting on anything, starter gear and flex plate are both new & show no scars, remove valve cover, the rockers are not hitting valve covers no broken valve springs, valve spring retainers not touching rocker arms, valve lash is perfect push rods are not hitting or rubbing anywhere on heads. I have the timing set at 35 degrees, it cranks, idles & runs smooth & perfect. The clanking noise does not effect anything, but I know it is not supposed to have it and we spent several hours trying to find where it is coming from & cannot find it. The sound coming out of the header does not sound like a "pop". Anybody have any ideas or suggestions?
P.S. The headers are not stainless steel but they have been JetHot coated & were not kept clean but they now have a silver coat of VHT Header Paint.