Tuning fork whine

I installed a new exhaust header in my 1972 Volvo 1800E. Now there is a tuning fork whine at around 2300-2700 RPMs. The header & exhaust system is well clamped/supported. It is driving me insane! The header vendor has “never heard of this problem” & has no idea. Any Ideas? Thanks

maury thibodeau




Wild guess, but it might be an improperly positioned piece of gasket sticking out into the exhaust header or exhaust pipe that vibrates rapidly as the exhaust pressure and flow increases; possible if a metal gasket is involved.