Lift pump?

[Signature620]

While the lift pump is running, grab the bottom of it and try to move it back and forth. If the sound of it changes then it is likely sucking air because they come loose from the top plate over time. If that's the case and it's done a lot of miles then it's probably worth just changing.

If you change it, use some ordinary 6 point m8x1.25 bolts instead of reusing those allen type bolts - The next guy will thank you.