ID - Thanks for your helpful post! The antenna is actually an outside antenna, 1/4 wave whip omni. The antenna is also shared with four other feeds, covering 127.85, 126.05, 125.25, 123.15, 128.875, 123.1, 123.075, 123.05, 123.025, 131.975, 120.8, 120.4, 134.9, 121.5, and the TEB freqs, and all coming from different directions (located about equidistant from TEB, LGA, EWR).
It's present much more strongly on some frequencies than others, and tested with a few receivers. You could be right about the product of two FM freqs. I don't have nearly enough knowledge about radio reception to properly analyze what the problem is, and unfortunately multiple directional antennas are out as the equipment has to be quite unobtrusive...it's hosted at an office I do a lot of business with. Any simple helical resonators or cavities available that I might try? And wouldn't my FM Notch filter have knocked down the FM sources you mention? Thanks for any further advice.
Skyshare - I'll remove KTEB Clearance Delivery from the scan soon per your request. I know it can block some things, but a lot of flights that operate out of KTEB are blocked on FlightAware so hearing a clearance can be the best way to actually track and match up a flight. We'll try for a bit without it and see how it goes.