Hi i'm building a chassis ear. It's an electret microphone that is attached to a metal clamp used to measure vibrations and noises.The first part is easy microphone and amplifier.
To sense vibration effectively (and accurately) its best to use a specialized sensor, electrets couple to air
well, but not the mounting itself (electret diaphragms are very thin).
To sense vibration of a solid object you ideally want a transducer with a high mass armature that will
try to stay still through inertia as the mounting point vibrates. Such a transducer will ignore ambient
noises in the air. The kind of exciter used to drive flat panels of material like a speaker spring to mind
as a possible transducer to experiment with.