It Starts at 2500 and continues, sounds exactly like detanotion. Very Slight. I say valve Guides cause when I had the header off I notice #2 valves had a small indention on the valves at the bottom of the guides and were shiny silver unilke all the others being dark black. This still occurs without throttle. The motor is a stock first gen b16

 

I need yalls help on this one.