Why would a gas tank pop on occasion, like if it's contracting or something. I sometimes hear it when driving and also when it's just sitting in the garage I'll on occasion just hear a pop or cracking sound coming from the area of it.

Probably need to replace the gas cap, need a vented gas cap.

Or your vent could be clogged !

Already replaced gas cap, still doing this. Where else would it have a vent ???

There is a vapor canister that looks like it comes apart to be able to replace the filter in it. They were in the front corner of the fender under the hood, also there is a vapor canister purge valve that probably should be replaced also..........https://www.carid.com/1987-chevy-el-camino-emissions-parts/standard-vapor-canister-components-64701766.html

Thanks ! I located the canister in the left front area of the front fender but how would one open this canister ? As for the purge valve no luck finding it. Do not know if it was removed St some time. Thank you for your help and any help on opening this canister is greatly appreciated.

Some of those canisters you have to replace, I just seen a filter replacement listed for it. The purge valve is in one of the vacuum lines that run to the canister, or suppose to be.

Yes suppose to be is right. However I found one line coming from the canister just there and not connected to anything. I guess some work was done at done time and just left there. As for the canister I cannot open it cause I am not sure how to go about it.any advise is greatly appreciated.