Constant electric Noise/Whine

Hello, and Good morning 5.0L Tech! So i'm finally getting around to tying up any odds or ends on my '90 LX. Ever since i purchased the vehicle it has made an electric whine i suppose you could call it. It comes from the rear of my vehicle next to my gas tank. It can be heard inside the vehicle and also outside the vehicle. The noise gets quieter when im driving, almost unnoticeable and when i rev up my engine it quiets down. Like the actual noise seems to become quieter not just my engine overpowering the noise. I've been given speculation on what it could be but not a reason as to why this is happening, the majority of people said it is likely my fuel pump as that is what it slightly sounds like and it is coming from around that general area. although im not sure how to go about the situation. Any advice or insight into this issue will be greatly appreciated! Thanks and have a wonderful day!

-Joe