I was flying last night and all of a sudden a heard a loud humming through the headset and as I scanned the gauges the Tach was pegged to the high side. It did this for just a short while and so I did not get to diagnose much. I went up this evening and flew for .3 hrs and it did it again but this time it was even a shorter span. I flew around for a while trying to get it to act up again, but it was getting dark and so I landed. Has anyone ever had this happen?