From what I can point out, it sounds like my fuel pump is getting weak. There is a real loud buzzing noise comeing from the rear of the car. When I turn the key it starts to buzz and turns off, then when I start it it begans to buzz again. Will a weak fuel pump contribute to poor fuel mileage? What is the avarge cost for a fuel pump in the bonne'*? Are they a pain to change?

Have you actually checked the fuel pressure at the rail? With a pressure gauge?

Granted, they do tend to get loud as they get weaker, but I say it would be wise to actually check the pressure before spending the time/money replacing the pump that you may or may not actually need to replace.

My $.02, keep the change.

As LH mentions.. it is recommended to check the pressure before replacing. Standard pumps seem to cost around $100-120 in my area. A failing fuel pump isn't normally viewed as contributing to excessive fuel consumption, if anything it may run you lean.

GM pumps are known to be noisy, and I've experienced a serious increase in noise before the drove me to change out the pump. Never failed..pressure checked out.. sheer noise level was too much to handle.

On the fuel consumption.. you may want to consider when you did your last tune up and how many miles are on your O2 sensor.