I get a noise from behind the radio of my Jeep wrangler 2003 that sounds like a vibrating spring that is hitting metal. I get it in the lower “harmonics” you get as you just shift into a lower gear. It doesn’t last long and goes away as you rev up in the gear.
Well it sounds like there’s something loose back there, or something is barely touching the back of the radio and resonating at certain frequencies. It shouldn’t be hard to pull the radio out and check or just move things around a little if it’s driving you crazy.
Any chance it could be coming from the exhaust system? Heat shields often come loose and make a metallic rattling sound. As you are driving, it may seem like it is coming from inside the car instead of underneath the car. Such a sound will only happen at certain ranges of rpm.
My advice is to look a little lower than the radio!
+1 to mleich. That’s a great point