Chevy s10 '98 metal popping sound from fuel tank after engine shut off.

Any recent engine repairs ? Trouble codes ?

did you change the fuel filter

EVAP system failure.

http://ricksfreeautorepairadvice.com/evaporative-emissions-system-primer/

sounds like a fuel tank inspection/flush or replacement is on the horizon.... sometimes dirty fuel has contaminated your tank or the tank itself is rusting from the inside out... either way it needs to be addressed... drain the tank analyse what gets drained for particles and water...send the tank to a radiator shop for a complete boil out/inspection....blow out the lines and replace the filter again along with the fuel bowl etc. after that all should be well?

No second fuel pump, note that it's common for the wire harness from the gas tank to the frame to go bad when manipulated to replace the fuel pump from the gas tank which is only a $15.00 replacement part. The fuel filter should also be replaced shortly after to ensure any dirt that got in the gas tank that the filter will collect will not restrict the flow of fuel to the engine. Good luck and keep me posted, be glad to answer any questions you may have.

Put the key into the ignition and turn it to the second position. This position will light up the dash lights but will not crank the engine.
Listen for a faint or soft humming sound coming from the rear of the vehicle, specifically the gas tank. This will happen almost immediately after you turn the key to the second position, so you'll have to listen closely and be ready for it. The humming is the sound of the fuel pump priming, or pressurizing, the fuel system. If you do not hear this sound, you may have a faulty fuel pump.

1. Check to make sure there is enough fuel in the gas tank. Although this may seem obvious, it happens to the best of us. If you're gas tank is near empty, the engine may not start. This happens more frequently in the winter time in cold climates; the low temperatures cause condensation to form on the inside of the gas tank. Since water doesn't burn, the fuel pump tries to draw in fuel and instead gets a mixture of water and gasoline and cannot get enough fuel to the engine for combustion.
   Check to see that the vehicle starts. Even if you don't hear the fuel pump priming, attempt to start the vehicle. If the engine won't turn over (start) and you haven't heard the fuel pump prime the system, it is a good indication that the fuel pump may have failed.
   
   Check the fuel pump fuse. If the fuse is blown, the fuel pump will not prime. Open the fuse box under the dash of your vehicle and locate the fuse for the fuel pump. Alternately, some vehicles locate the fuel pump fuse in a fuse box under the hood. Remove the fuse box cover (specific removal will vary according to the vehicle). Check the fuse to see if the metal strip inside the fuse has popped. Replace the fuse if the metal strip has popped; if it hasn't popped, it is most likely your fuel pump itself that has failed.
   

Youre gauge is controlled by a plunger in the fuel tank which is attached to the sensor and the fuel gauge. it sounds like when the plunger goes down half way its either getting stuck down lower then it should. Needs replacing. Any mechanic can do this install for you.

Just a thought...did you buy a key type gas tank cap...maybe it is defective or the wrong one and does not allow venting properly and the tank pops when pressure is relieved. You could also have a bad evaporative cannister.

there is no fuel pump shutoff on this truck, if the fuse and relay are good there is a 99.9% chance your fuel pump is gone bad. they usually start to give off a louder sound from the tank and then they quit shortly after.

I had the same problem with my 1998 Cavalier and it was the wiring harness which fortunately is under recall if you call your Chevrolet dealership in your area.