Question

A vibrating simple pendulum does not produce any sound why?

Answer 1

The shorter a pendulum is, the faster it swings. If it swings faster than about 20 swings per second, it'll produce a sound that your ears can hear. That would be a pendulum that's something like 0.00065 CM long ! Good luck with your construction.

Answer 2

The frequency of vibrations produced by a pendulum does not fall under human ear's audible range, so we do not hear the sound produced due to these vibrations.

I think this could help you :)