We have a little unit with a CD player in our bedroom that also does this erratically and unpredictably. It seems to be set off by such diverse events such as a sparrow farting or a bumble bee in the distance and it is somewhat disconcerting to be awoken by a variety of music from Beethoven's 9th to Led Zep's "Whole lotta love" in the middle of the night (we are quite eclectic in our tastes).

Strange...

Peace, moo