*VERY* Noisy Fuel pump

Well I have a 2000 Rodeo 3.2L. I am in the military and currently in Thailand with it. I just got back from a trip in the mountains up north, big steep mountains ans deep vallies. When we finally got to where we were going I rolled down my window to talk to my buddy, I could barely hear him over the fuel pump. It didn't drive any different it felt the same. I made it all the way back 80 mile 4 hours, just to give you and idea of the mountain trails we were on. Any idea of what this noise might be from? I am pretty good on doing work myself as long as it's not to much disassembly, but labor here is dirt cheap if I need to get something done. Thanks for you help

I get a really high pitched loud whine from my fuel pump when I'm in the mountains for some reason (over 9kft elevation). Doesnt do it all the time though. Its been doing it for the 3 yrs I've had the truck and still going so no idea if its a sign of things to come.