i've been trying to figure out the cause of this one for months, and finally found it.
i edit my audio items while the playback cursor loops the relevant section.
this means that i'm often cutting, moving, pasting, stretching, and otherwise editing items that are being played.
many, many times per session, i get a massive BANG that clips out my track (and automutes it, if that param is engaged).
today, while testing, i learned that this only happens to STRETCHED items (either by playrate or by stretch markers).
here's a gif. no master fx, track gain neutral, no track fx. watch the meter. it clips to 15db first, then to 55db.
if you have a reverb on your track when you do this, it's utter insanity.
at the end of this gif, i demonstrate how this doesn't seem to happen to non-stretched audio (and this is a wav)
i don't care how this is solved, but my suggestion would be to disallow REAPER from attempting to play items that are being "held" by the mouse. wait for the user to release the item before attempting to play, and apply a tiny fade to items that are newly dropped over a moving play cursor.