“Is it possible KNRQ on 103.7 is somehow “too hot” and that’s causing the harmonic interference? I know nothing about radio engineering but every time I tune 103.7 now it seems WAY “louder” than any other station.”
If they are over modulating, their signal becomes wider on the dial than it should be and can cause lots of interference. And yes, it will be louder.
Quick primer for non engineers in analog FM:
Frequency modulation is achieved by varying the carrier frequency around center frequency. The carrier moves back and forth from center at a rate dependent on the frequencies of the modulating information. The distance from center that the carrier moves is determined by the amplitude of the modulating signal. 100% modulation is defined as 75 kHz of deviation. So over modulation means the signal is moving further than 75 kHz from center. Since the channel is only 200 kHz wide, 100 each side of center, you can see how it will splatter to adjacent channels when over modulating. It also can create spurious harmonics that wouldn’t be created had the modulated envelope remain inside its boundaries.