I've had a similar experience making an FM transmitter. I used a small air coil inductor that wasn't well secured to the PCB as part of the resonating circuit.

I've had a similar experience making an FM transmitter. I used a small air coil inductor that wasn't well secured to the PCB as part of the resonating circuit. My FM tuner would pick up ambient noise since the small sound vibrations would ever so slightly change the size of the inductor, modulating the frequency. Ceramic capacitors also have this problem. The small metal 'fingers' are susceptible to vibrations which change the plate distances, and thus the capacitance. Use your imagination to think about cases when this might be of interest for certain groups!