Microphonics

A system sufficiently susceptible to microphonics could experience audio feedback, and make noises if jarred or bumped.

To minimize these effects, some vacuum tubes were made with thicker internal insulating plates and more supports,[4] and tube-socket assemblies were sometimes shock-mounted by means of small rubber grommets placed in the screw holes to isolate them from vibration.

Guitar amplifiers that incorporate the electronic chassis into the same cabinet as the speaker are susceptible to microphonics.

Unwanted microphonics-related audible distortions can often be alleviated by using commercially available vacuum tube mechanical dampers.

Before the introduction of solid-state charge-coupled device (CCD) sensors to produce the image, vacuum tubes performed this task.

Audio vacuum tube with externally fitted microphonics damper
Radio and TV repairman's tool for testing microphony in vacuum tubes. The black rubber grommet gives the tube a firm but safe impact. Pen for scale.