I have a 912UL in my Kitfox and last night while flying I got a loud noise thru my headset. It would come and go and everytime this loud noise would happen my tach which is a Rotax unit would peg to full RPM then the noise would stop and the tach would go back to normal. It would cycle back and forth. I cut off the alt. circuit and then turned it back on and it stopped. Several minutes later it started this again and I did the same thing and it stopped. I landed and am wondering where to start looking for a problem. Any help would be appreciated. Thanks