Hi Peter, Welcome to the madhouse. Now, we dont care if you are a relocated pommy, as long as you live in Queensland then you're one of us.
If you were a Victorian..then maybe we'd chat to ya...maybe not...If you were Victorian and had a Chevy in ya cobra..well then ...
Now..to your tank. In tank pumps set up a resonance..a high frequency vibration if you will. With production tanks (mostly plastic) this isnt a problem, but with metal tanks, this resonance can become audible.
The resonance becomes audible if the tank touches some other fixed chassis component..ie a bracket/chassis rail etc. Obviously going uphill caused the fuel to move back in the tank, maybe causing the tank to move in its mounting ever so slightly, thereby touching some fixed component.
Thats why it is a good idea to put thin rubber gaskets under tank mounting flanges if using in tank pumps.
Few years back a mate with cobra used to get this funny noise from the back end. After months of searching we found the problem to be the fuel filler tube that entered the tank. He had not allowed enough gap between the tank filler tube (the 2"pipe welded to the tank) and the pipe to which it joined with a short length of hose from the fuel filler.
On some throttle openings the two metal pipes would just touch causing the resonance to become audible. The movement of the tank was barely noticable but sufficient for those two pipes to touch.
A hacksaw to remove 1/8" of pipe fixed an annoying problem.
Maybe something similiar...worth a look anyways.
Make sure you keep in touch