Thunk from sitting truck

Lately I've heard an odd hollow, metallic sounding thunk from the truck several times while not running and I think once while idling for varying periods of time. It sounds exactly like and old square sided metal gas cans contracting and expanding due to temp fluctuations. Only one thunk per day or maybe one AM and one PM use. But I think my tank is plastic. I've never heard it before in almost 14 years. I'm a bit perplexed at what the sound would be. I'm wondering if it is the muffler but that's open via the tail pipe so it shouldn't be expanding or contracting. I did notice a fair amount of water draining from the weep hole in the muffler the other day when parked uphill on a paved drive. Truck runs/drives fine. Any ideas?
 
Turn the radio up, run it until it breaks. Then you know what to fix. Seriously, after 14 years, if it runs, you are doing pretty good.
 

I had a mysterious noise in my truck not too long ago. Showed up only occasionally, and didn't seem to have any real pattern to it. The noise didn't sound real serious, so I didn't dig too deep trying to find it, but it was still annoying. Turned out that some stuff in the tool box had shifted just a bit, which then allowed a can of PB Blaster to roll around freely.
 

I would suspect a heat shield that has gotten deformed by heat. The boiler in my house stated to make that sort of sound 20 min after shutting down. My oil burner guy told me probably the heat exchanger cover got deformed. It was 25 years old so I replaced it.
 
That's the method I've used to "fix" my 1999 E150... I'll take a closer look for noises that seem to originate in the engine or transmission, but rattles, squeaks, and thunks all get the radio fix.
 
I never listen to the radio. Too much yack--not enough good music. Besides the thunk occurs after you've parked it and are perhaps unloading some stuff.
 
When I was with GM, I sold a lady a new Chevy minivan. A week later, she came back, madder than hell and complained about a rattle under the floor.

We checked it out in the shop and found a jar of pickles rolling around under the passenger seat.
 
I had an empty 250 gallon fuel barrel on the east side of a storage shed that would make a small boom when it expanded every morning. Every time it sounded off the hogs would go a running across the feedlot, then come casually wandering back to the feeders. It was a daily routine for all of one winter. Is there a dented fender in your pickup that flexes and pops in or out when it warms up? It's the only thing I can think of. Jim
 
Mine will make several "tinks" or "thunks" I guess, over an hour or so, while sitting after it's been thoroughly warmed up.

11 years old, 215,000 miles on it.

Whatever it is, it's just something hot that's been deformed by age and thousands of heat/cool cycles, and is contracting as the truck cools.

I really haven't done much to figure out what it is. If it's important it will fall off then I will know what to fix, or I'll buy a new truck.
 
I agree with mkirsch, something hot cooling off... ...the catalytic converters will make lots of noise when cooling off, even on new vehicles.
 
Maybe it is a leaf spring or shackle moving and making a noise?

I bought my first ever new pickup and after a few days it made a clunk every time I hit a good bump......Found out that it is the ball hitch that I installed in the receiver!!! A little gravel and dirt and it'll stop soon.....
 
(quoted from post at 10:07:07 10/24/14) Expanding/contracting of the tank maybe. Leave your gas cap loose, see if it solves it.

How far could he drive with a tank that isn't venting?
 
My uncle had a noise once in a while so he turned radio up also, few days later he had his 5th wheel camper hooked up driving to the lake and his rear wheel fell off. Its proly exhaust but you should atleast find out for shure. Don't ignore it find it and fix it!
 
Many years ago as a teen,I drove to my buddies farm and went with him for the nite. Drove back home late in the night and when I shut of the car there was thumping comeing from under the hood. Next morning I raised the hood and out jumped a chicken ,all fine and well. Must have felt like being cooked alive.
 
My dad has a 97 chevy truck and it has a vented gas tank, the vent in the gas cap is plugged and after you drive the truck and park it the tank will make a thunk noise. Its the gas tank popping back out from the vacuum in it.
 

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