Question

We hear the sound produced by humming bees while the sound of vibrating pendulum is not heard

Answer 1

The frequency of humming bee is between the audible range the vibrating pendulum has a very low frequency which os not between the audible range.

Answer 2

First, let's define frequency. It is no of vibrations produced per sec.

Humans can hear only sound of those material whose frequency is 20Hz to 20000Hz. If the frequency of the body is less or greater than this human ears are unable to perceive sound.

So if the frequency of pendulum is less or greater than this range you cannot hear the sound produced by it.