I have a 94 with dual tanks. With the igntion on and i switch back and forth from tank to tank. the rear sending unit sound fine but the front one does not run as smoothly but both tanks are full and the truck runs great on both tanks. is this going to be the start of a failing sending unit.

 

You could try checking the pressure at the rail and see if the noisy pump is not putting out as much pressure.

SL

 

I have the same style of truck. How many fuel pumps are there? I've heard everything from 1 to 3 (One per Tank and one shared). My guess is 2, but 3 would help me answer another problem

 

There is only 2 two pumps. One at each tank.

Thanks for the feed back.