Other lower frequencies for a Crystal

[eedac]

I used a FM audio transmission IC. A 7.6MHz crystal clocks the system and to be divided as a 19kHz-pilot.

But I found some other lower frequencies (600Hz, and 1kHz) accompanied with the pilot. It is generated from the crystal.

I tried to change the caps between the crystal and ground, frequencies would exist......what's go on? do any idea?

Thanks!!