noisy fuel pump when hot???

I have a 91 laredo 4.0 that the fuel pump gets really noisy while on the trail. It seems to only act up on initial start up after the jeep sits for awhile, 15-20 min. It also idles rough while this is happening, and I get a stale, almost sweet smell of fuel under the hood. This never happens during normal driving around town, just on the trail. Have replaced the fuel pump and the gas cap, but problem is still there. Maybe vapor canister, fuel pressure reg. I don't know, any help would be greatly appreciated.