Also, it is not mandatory for Class A and LPTV to convert to digital in February, 2009. So if there is a Class A/LPTV signal on channel 6, 87.75 TV audio would pose as an interference source. I don't know if it's still active, but at one time there used to be an LPTV on channel 6 east of downtown that relayed "The Box" or some knockoff sat-fed music video junk, and I think changed sat format later.
In fact, the LPTV lobby, what lobby there is for such, has filed complaints based on the digital-to-analog converter boxes that allow over-the-air DTV signals to be viewed on analog televisions. They state that since most LPTV signals are not carried by cable providers, this violates the All-Channel Receiver Act (ACRA).