HELP!! 1997 chevy making weird NOISE!!

1997 chevy cheyene 5.7L 350 Truck has 140,000 miles. I noticed my truck hasnt really been running right lately. When shifting in low gears it makes a wierd noise. Now it is worse and sounds like a low hummin sound. So I put it in park and got out and noticed I couldnt hear the low hummin sound from the motor, but when I got under the cab near the rear tires I could hear the hummin sound a lot better. Im not sure what the problem is, but sounds like tranny to me. Any suggestions??

Try this-- With engine oiff-- listen if it hums just by turning ignition key on.... see if hum lasts for 2 seconds...then quits.....

There are a lot of fuel pumps that hum good and loud- and does not necessarily mean anything is wrong.

A fuel pressure check will confirm if this is the cause of "not running right"

Yea I noticed it IS the fuel pump. But why is it running constantly. I've never seen it do this before. I installed this fuel pump about a year ago myself and havent had any problems with it. Could it be shorting out?? Should I check the wires?

with the key on but the engine not running, the pump will run and then shut off. with the engine running, the pump will run all the time. I have had some trucks that you could hear the pump running over the engine.