[DeTomaso] Exhaust Valve Not Closing?

[Art Stephens]

     A couple weeks ago I missed a shift and surely over revved the engine.  The engine was making all kinds of racket for a couple minutes and then the noise stopped.  Hmmm?  The engine runs fine till I run it hard and then it sometimes does the same thing again.  It sounds to me like an exhaust valve is not completely closing?  Any ideas as to what is going on?

Thanks,
Art