I've always had this problem. ANd then once their stuck, I'm humming all around the house.
DH thinks it's funny, so he'll hum a few notes of some really dumb song (like, oh, The Oscar Mayer Balogna song) then just wait paitently -- sure enough, give me a minute and I'll have it stuck in my head and be humming it!
Ugh! THe tricks a DH learns to play on you in 20+ years - just no fair, LOL!!