I have a knocking noise coming from what seems to be the fuel rail on my '99.
A screwdriver held to the ear seems to confirm; I can also feel the knocking with a finger.

I run high impedance RC 550s, stock fuel rail and pump.

This doesn't sound like lifter noise, and is too low pitched and rev independant to be rod knock.

Any ideas what the hell this could be?

 

My 550cc injectors tick a little bit but nothing that would be a knocking.

 

You are welcome to pull the one off of my 99 and give it a try... she's just sitting here waiting on lights, fender, bumper, control arms... ect.

I would be willing to bet that it could be "overdriven" with the extra flow and pressure.

Should be home in G'town after 7 and will be under the other car installing my adaptronic.

Cheers,
Prospero