Had a propane cannon fire right under me as I dropped over a hedgerow while spraying a field - couldn't see it from the back side & I forgot it was there while working another area, that'll get your attention!
Had an FE that thought he heard a funny noise coming from the fwd transmission area of a Chinook, we made a precautionary landing in a parking lot. Turned out to be the retaining latch for the upper cabin door that holds it in the open position vibrating, but better safe than sorry for sure.