Could be brickwalling because the top of the waveform is squared off (clipping) but the other noise is weird. I'd look at power/cabling first.
SPL did not exceed the rating of the microphone, did it? Too loud an input signal would saturate the front end of the mic, and cause brickwalling at that stage (hence attenuators on mics).
Does this happen consistantly, or was this a one time, non-duplicatable, freak occurance Schwilly (and did you wash those SHEETS yet?)
Rick