I have a 97 K1500 Suburban with 175K. I have noticed that I recently developed a "hollow clicking" or "metallic rattle" sound. It sounds as if it is coming from under the truck towards the drivers side, middle to rear of the truck. I can hear it driving while driving at low speeds 20 m.P.H or slower. I have found that the noise goes away if I accelerate but happens only when not accelerating. Braking does not affect the noise what so ever. It almost sounds like a loose center cap rattling, but I know that's not it. Hopefully, someone has some idea(s) and advice on what I need to be looking for. Thanks.
There is a tool you might be able to borrow or rent from an auto parts store that borrows them called the "Chassis Ear". It is a set of six microphones, a switch box, and headphones. You clip the microphones to suspect points, then drive around while listening with the headphones. You can move the microphones around to zero in on the source of the noise. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment mechanics use it to find rattles, squeaks, and other noises.
There is a newer version of this tool that has four wireless microphones and two with wires. If you can find that one, use one of the velcro straps to tie two of them to the front of the drive shaft. Place them across from each other so it stays in balance.
Look for anything that fell down and is rubbing on the drive shaft. I've even had tree branches get caught up in there and snap against the balancing weights.
Use some type of metal to insulate one microphone and wire it around the exhaust pipe. Those pipes have been known to cause pinging noises when they heat up and cool down but you typically won't hear that while driving.