"Oil-canning" sound?

[Kurt Combs]

This is strange, and I may be the only person with this problem. Every time I accelerate or decelerate I get what I call an oil-can sound. This is definitely sheet metal acting like a drum skin, but I can't figure out what is doing it. I thought it was the seat back coming in contact with the gas tank, but I changed seats and it still does it. It makes the sound with or without a passenger. Any ideas where I should start looking?

Thanks for all the help so far! I am on the road again and getting comments like, "clean truck". This is a truck that had grass growing in the bed two month ago! I couldn't have done it without all the help I got on this site.

Kurt

[qman]

Exhaust Leak. Maybe where the header pipe connects to the manifold. I only say thing cause your description of the sound is exactly like one I have with my leak.

[jzjames]

Is it your gas tank sending unit inside the tank? Mine makes a noise like that also. Its like tapping against the side of the tank I think.

[Kurt Combs]

The sound could be from inside the gas tank, but I think it is a big flat piece of sheet metal that is flexing in and out. The question is where? I went out and look at the truck after my first post and I noticed that the seat contacts the cab at the top....could be it. The usual solution to sheet metal making that sound is to smack it with a hammer and dent it, but I don't really want to smack the cab of the truck like that where it shows. I will take it for a drive with something between the seat and the cab and see if that make any difference.

Thanks for the posts.

Kurt

[Aubrey]

My seat back touchs the cab, but I don't get any noise from it. It has to be all the way back to give room for the beer keg I carry around with me.

[FORDification]

Does your floorpan have some rust? If so, and it's weakened a bit, maybe the forces caused from acceleration/deceleration which cause you to lean forward/back in the seat is causing the floorpan to distort a little bit. Try rocking back/forth in your seat and see if you can duplicate the sound.

Another thought...could it possibly be your fuel tank itself? I don't think acceleration/deceleration by themselves would cause it to flex, but sometimes if you have a non-vented cap on a tank meant to have one some vacuum gets built up inside, and might make that sound as it escapes. Similarly, on a hot day some heat buildup might occur and cause the tank to make that sound.

[Kurt Combs]

Thanks everyone for the responses so far.

This sound is coming from the back of the cab, or the bed floor, or the front of the bed. Maybe the bed is lose? Light acceleration or braking will cause it. Also a slight turn that would twist the frame or body, causes it. Really strange. I will unload the extra seat in the bed at the dump and jump up and down on the bed and see if it is coming from there. Maybe the gas tank has been replaced in a bind, if that is possible. More later after I have a chance to investigate further.