The squeak

Several years ago a squeak first sounded in my car. It sounded like the noise was coming from inside near the back. But after many attempts to silence the irritation it Very slowly grew only worse. There was no squeak when the car was rolling along on smooth pavement. Sometimes it squeaked often, sometimes less. Initially it required hitting a big bump to produce the sound, but over time it occurred easier and easier. Guess what it turned out to be? There was a speaker panel that had slowly worked loose and only made noise when moved in a specific way. Simply tightening the screws fixed the problem. It just took a while to find which screws.