High pitched noise in fuel tank

[President]

Hey guys. Bought my K9 Busa new and its been faultless. Recently though it has developed this strange high pitched whining sound that is coming from within the fuel tank. Engine starts fine but the sound appears about a second later. It disappears after about 15 minutes of riding and doesn't reappear till next morning when cold again. No problems with power or startup. Can you tell me what's in there (fuel pump?) that could be responsible and is it hard to replace? Have lifted the tank on its prop and the noise is clearly inside the tank.