High pitch Sound

I guys I am new here. I just picked up a 2012 Audi A3 TDI with 80K. Love the car and it's my 1s car. Today I noticed when turning on the car I hear a high pitch sound. To me is sounds like it could be the fuel pump motor? Once the motor is shut down the sound will turn off 5 sec later. I don't remember hearing this sound before. Is this sound normal? Is my fuel pump or some other electric motor just being loud? Looking forward to learning a lot from you guys.

Update from reading more about this whining sound I assume it's my fuel pump. I have an appointment to have a fuel filter changed. Anyone know how much a fuel pump cost to have replaced? Is the car safe to drive or should I park it till I see my mechanic?

Going to dinner tonight I decided to take the car. I noticed it a high pitch frequency sound coming from under the motor on driver side. If I get down next to the motor I can hear it well. Starting to think it's not fuel pump. The sound will stay on after the motor is shut down then fade out. Anyone had this issue or heard of it?

Found out on this forum the the high pitch frequency is normal. I never picked up on it before. Nothing like an EEEEEEEE.... to make for little concern.