This was produced by tapping on a stethoscope which had an earbud pressed against a Shure SM57 mic. Low pass filter applied, as well as compression and a gate. Chorus added. Used a recording cassette deck as a preamp going into an M-Audio Audiophile USB soundcard.
Note: If you're having problems listening to this clip, the cutoff frequency of your speaker set may be too high(solution: new speakers). The signal strength exists almost entirely in the very low frequencies, so you may need a sub-woofer to hear it. Otherwise, try turning your speaker volume all the way up. Doing so may saturate the signal and at least allow you to hear the harmonics of the signal caused by the distortion. I don't recommend it, but you'll at least maybe be able to hear something.