When you refer to channel 8 I assume you are speaking of WTNH, real channel 10 (virtual channel 8.1). If your antenna is pointed toward NYC (about 250°) reception of WTNH would be problematic. Real channel 10 would not be a likely source of interference to real channel 7.
Real channel 7 is not usually affected by FM stations, but you have a very strong signal from WEBE-FM, 107.9 MHz on an azimuth of 254° (compass). An FM trap would not hurt, and, they're not expensive or hard to install. Example,
Radio Shack Cat# 15-024.
How difficult would it be to test reception with the antenna outside, on the roof?