Clunk / Rattle In Rear Of Truck

Wingnutt · July 12, 2009

Truck specs: '99 NBS 1500 Silverado 1500 ext cab / short bed 4x4 5.3 auto, 135k miles.

Problem: when I hit a bump or large expansion joint I can hear a clunk / rattle from the rear of truck. Here's the interesting part, when going over a small bump the sound is closer to a rattle ie. it sounds like something light, but if I hit a larger bump or something that jolts the truck, the rattle sounds more like a clunk, the sound is more like a heavier part would make. I've taken the tailgate off, but the sound is still there. I rotated the tires last night and found evidence where the parking brake cables were moving around in their bracket, so I zip-tied them in place and went for a drive and the noise is still there. I've checked the exhaust by both kicking it and moving it but it made no sounds. Same with the bed, fuel tank and spare tire...no movement and no noise. The shocks are not broken, nor can I find where anything else was moving. The truck makes the sound more when the weather is warmer than when it is colder (yes I've been trying to track this down for a while now). The only other bit of information that I have is that a month or so ago I was forced to drive through a flooded area of road at 45mph. This produced the expected huge splash and tidal wave but it also quieted the clunking / rattling sound for about a month. I haven't had the time to check the torque on the skid plate mounting hardware yet, but the skid plates are located under the front half of the truck, and the sound "appears" to be coming from the rear.

This is driving me nuts. I hate driving a truck that sounds like a toolbox rolling down a flight of steps every time I hit a bump!

Any suggestions will be greatly appreciated at this point!

TIA

bill190 · July 12, 2009

All right! Time to bring out the Advanced Noise Detection Finding Kit (ANDFK)!

My usual trick is to get an empty paper towel roller, place one end to your ear, then point the other end at various places to find the noise...

However I don't think it would be safe to use this method for this problem!

Perhaps you can rig up a microphone under the truck and run a wire up through an open window into the cab, then use a cheap amplifier and speaker in the cab to listen to the sounds from the microphone?

Then drive around and listen. Then move the microphone forward a couple of feet and see if it gets louder.

Then try 4 feet back.

Move it forwards/backwards until you find the location which makes the loudest noise.

Then try moving it left/right until you find the spot making the loudest noise.

Then that should be the area of the trouble.

Wingnutt · July 28, 2009

Here's a little update. I took the tailgate off and had a friend lay face down in the bed looking under the truck while I drove over a few bumps to get the noise to appear. He said that he couldn't pinpoint the noise, but everything looked nice and tight with nothing moving that wasn't supposed to move. We went over all the body, spring and axle nuts and blots and everything was tight. Only other option seems to be the shocks. I'll change them out at the end of the month and hope for the best.