Back when you could still see test patterns in the wee hours, some stations broadcast music over the TP rather than tones, especially in the period prior to sign-on. (Tones would still be used during actual "tests," of course.) The most famous example of this is probably WCBS-2 in New York, which used music over its classic bulls-eye TP in the brief period between the end of the Late, Late Show (or was it the Late, Late, LATE Show?) and the start of the morning schedule. What are some others? What type of music did they use (I seem to recall from the stations I saw, it was often inoffensive "easy listening" or "101 Strings" type stuff) and was it generated in-house or was a local FM station rebroadcast?