It's been discussed many many times before. 87.7 is the audio of Channel 6 VHF (TV). The video of Channel 6 doesn't get out all that far, and I believe it just shows test bars or infomercials. The audio carrier is on 87.76 to be exact and has been leased to a Russian broadcaster which operates 24-7. The FM signal gets out very far. They broadcast from the top of the Citicorp building in Long Island City, Queens.
Often on Friday and Saturday and sometimes even Sunday nights, they have some great dance music playing nonstop, not all of it Russian.