My over-rev buzzer recently started going off at 5k. I let off at 5 and it stopped when it went below and came back after going over 5 again. None of the warning lights go off so I think it is the over-rev buzzer and not coolant or oil warning.

 

I keep reading that the RPM at which that buzzer turns on can be adjusted. Search for that. First, however, I would look into a way to make sure your tach is actually correct.

 

My buzzer doesnt even work.