After the initial "Oh s**t!!!", I began to trouble shoot. No increased vibration, all engine parameters in the green, no loss of power. What the heck?
I concluded that I either blew out an exhaust gasket or one of my exhaust hangars had busticated.
I landed without incident, also noted that I had not soiled my underwear, and proceeded to remove the cowl to check things over. Everything was secure and no squawks were noted. Again, what the heck.
Then I remembered that after a fight a while ago I had forgotten to turn off my ANR headset. I returned several hours later to find that the headset was still working, so I have been blissfully flying along with a low headset battery.
What had happened was that battery went tango uniform on me and it cutting out, with the subsequent increase in perceived cabin noise, is what freaked me out.
One good thing out of all this was that I flew the plane after the onset of "the incident" and worked the problem. Turned out to be a good exercise.
But boy, do I feel stupid!
