Has any of these happened to you:
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Somewhere in the background you hear a song (barely) on the radio. You THINK you know what it is and start singing it in your head, but when you get closer, it’s another song entirely and your brain vapor locks for a second as you adjust.
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Above scenario, but you hear the song on an off beat and have trouble locking it down.
Also, just for fun, any time you hear any word/words that rhyme with/or are similiar to “other” (brother, mother, lover, another, etc), substitute “Tom Smothers”.
Yeah, both number one and number two. That last one, I’ll have to try it sometime 
Well Mr., I’m not sure if this is what you’re after, but I have trouble with Pink Floyd’s Another Brick In The Wall. To explain…
You know that chorded guitar part that comes just before the shouted Hey! Teacher!..?. Well, I have trouble “counting” the number of repeats before the shout and I always come in a beat too early.
I have since learned that when I am singing along with it on my car radio to actually count the measures (4 I believe - it’s been a while), and then I come in with the singer.
Quasi
I experienced both tonight. I was at my friend’s house, and his parents were having a party in the basement. I would start singing along and then it would be a different song entirely. For instance, I started singing “Hungry Like a Wolf” to “You Dropped a Bomb on Me.”
I get #2 a lot…
#3 not as much… it takes a while to get things moving