In the first episode aired, the contestant gave a clue that was bleeped, and the celebrity answered right away. I did a quick flip-back in my DVR and realized the contestant sang about three words from Steve Miller ("fly like an..."). Obviously the 1kHz tone was all that was keeping them from forking over royalties (although debatable, but lawyers must be lawyers).
In this afternoon's episode (first-run for me, so I won't spoil) they seemed to dub in the countdown music to blank out a sung clue. But an interesting admonition came up: in a category of things associated with [a certain singer], Mike Richards said, "remember, no singing."
Let's set aside the no-singing rule from the Rock & Roll Pyramid pilot, because that was not allowed for an entirely different reason. But it would have been odd, in the heat of trying to finish the 7-out-of-7, to hum/sing a few notes and be cuckooed for it. (And I know that "Favorite Things" was buzzed when the clues from "Sound of Music" were sung, but those broke other rules.)
It's an odd overprotective rule, but it seems to constrain a logical expression of a clue. I understand why it's in place, but shame that overlitigiousness is rewarded and affects totally unrelated form of entertainment.