Most of what I've heard has leant towards it being either "mouth music" or the result of translated/reworded songs having nonsense sections added in to make the meter work.

I also rather like the version that a friend of mine espouses: Drunks in a pub, forgetting and mishearing and slurring the words, and then later (after sobering up) realizing that "arrruheamuuuuuur" just doesn't have the same 'zing' as "whack-fol-a-tooral-aye-ay"

M