High pitched whisle from underneath right rear seat on 2008 Volkswagen Jetta

Purchased a used 2008 Jetta SEL the other day and I noticed a high pitched whisle or whine coming from underneath the right rear seat. The noise changes in pitch when the throttle is pressed. It looks to me like it's coming from the fuel line but I can't be sure. Please help.

Asked by for the 2008 Volkswagen Jetta