Ideally, vehicle would only make two kinds of noise: the “vroom” of a revving engine, and maybe a pleasantly deep burble at idle. Beyond that, every single noise a vehicle makes is either an annoyance or a sign that something has gone wrong. Suspension squeaks are tremendously common on older vehicles for the same reason that door and floor squeaks are common on older houses. Most aren’t signs of terminal failure, but all make your prize ride sound like an ailing bucket on its last leg.
The Nature of Squeaks
A squeak or chirp is a high frequency sound wave, and requires the same thing that all high frequency waves to: a very rapidly oscillating or vibrating surface that vibrates the air. In an automobile, the inevitable cause of squeaking is a surface moving against another surface, which grabs and releases it thousands of times a second. Anywhere two parts come into contact is suspect, but especially so are places where metal itself vibrates because of contact with other metal, or with rubber. Of course, in application, that means practically every part of your suspension, which can contain dozens or hundreds of moving parts.