2000 Silverado weird sound problem...HELP!!

First of all this post is for my father-in-laws truck and I am stuck on what the problem may be. Its a 2000 Silverado 1500 w/5.3 motor. Here is the problem. The truck runs fine and doesnt seem to be any different from any other time, but the truck makes a high pitched tone while running and someone told my father-in-law it was the fuel pump and others said it was the gas cap. The fuel pump was replaced about a year ago by someone else. From past issues with other vehicles I always had problems with a vehicle running when the fuel pump was going out.....ie: rough running, hesitation, etc. Nothing on this truck is running bad. The noise is definately coming from the gas tank area but just cant justify replacing a $300.00 part without knowing for sure if that is it. My father-in-law said he took the gas cap off and put it back on and the noise went away for a few hours and came back. Should I try a new cap? If anyone could give me some ideas on where to start I would appreciate it.

It is the fuel pump. My fuel pump never whined until it crapped out at 95k. I replaced it and now my new one does whine every now and then. I say you are fine, nothing to worry about.

You could try replacing the fuel filter just for peace of mind.

I would guess its the fuel pump. All of them get noisy after some time and some are louder than others.

well I think I`d do the cap first if you think it may be the culprit. Do a pressure check to see if it i up to snuff.

Past experience just a matter of time till pump fails. Doing this yourself is not a huge job. Make sure you wash good underneath first.

Done a couple this year. You can buy just the pump on ebay no need to buy whole module. Costs around 40 dollars,easy to swap out.