Havin’ a toot.
is it Ella?
Your toilet wants you to play Musical Chairs.
You’re not sitting down before the music stops, are you?
Probably the kid in the apartment below yours has his boombox propped against hs toilet and the sound vibrations run up the pipe.
Here’s a tangent. I notice that if my electric guitar connection is a bit loose, that I pick up some sort of radio broadcast through the amp. 
Breaking news!
First, publicly appreciating this beautiful phrase.
Second, my office photocopier makes a distinctive set of tones that doesn’t sound like music, but I hum a little song over it, and when I hum that song outside the copy room, some of my coworkers ask, “What is that? Where do I know it from?”
FWIW I live in a detached ranch house with a basement and I always seem to be hearing talking and/or music in the bathroom pipes. I figure it’s a combination of air flow and my own tinnitus.
Just to be clear, it is not a plexiglas toilet, right?
Have you considered the possibility that your toilet is haunted?
No such thing as ghosts. Could be heavy-metal poisoning though…
Your bathroom may have been designed by Bergholt Stuttley Johnson. If this is the case, I’d suggest nailing a large quantity of planks in front of the door. And don’t use the bath.
Well, that’s just bloody stupid!
(Nice username/post subject convergence, though!)
And watch out for weird noises–oh yeah. Right. I forgot.