It's probably "another brick in the wall part 2".
Does it go "we don't need no education?" in the chorus?
If there's lots of clock sounds (ringing, ticking, etc) it's Time
If the song starts out with money sounds, it's Money
If it starts out with what sounds like acousic guitar over an old radio, it's Wish You Were Here
Comfortably Numb repeats the title in the chorus several times, so it's pretty obvious. Same with Us and Them.
The only other ones that get radio play are "Shine on you crazy diamond" (again, in the chrous and its easy to understand) and "Have a Cigar (song has long instrumental intro, followed by 'Have a Cigar boy, you're gonna go far...').
Edit: Could also be Brain Damage / Eclipse. The local classic rock station plays that combo together, never alone.