When I noticed some FM on the Radio Systems, I Am Radio (a.k.a. updated Talking House), TX, I grounded the case of the main crystal to chassis ground and that reduced the FM to better than 1/2 of what it was. The 13.560MHz AM Pixie-like TX I have, the main crystal is 13.560MHz (Thank you Fearless Fred on that one!). That crystal is also tied to chassis ground. On FM listening, I really have to crank the volume all the way to just hear it. It's better than any commercial AM TX gear that I have. You might want to give that I try. Where did I get the idea from? Before ICF (International Crystal Manufacturer.), closed up, I asked their engineers if that was a good practice to ground crystal cases, and they recommend that indeed.