Ok, I need some help I have '89 560sel. I have a weird noise coming from my fuel pump not the regular noise,, ( i know that the fuel pump is supposed to make some noise) this noise can be heard in the cabin and its kind of like a bee buzzing but it buzzes stops for a sec and buzzes a little some more. I cant really explain how it sounds. I am wondering what can be wrong with my fuel pump and also where is the cheapest place that I can find a fuel pump and how much will it cost.

Thanks alot in advance,