Well thanks to the boys at ASG, we pulled the pump out.. the butyl rubber I'd used to insulate the pump had deteriorated, and pieces of it were sitting on the bottom of the tank. This was blocking the strainer!

The fuel pressure was flickering all over the place too, according to the gauge we hooked up... it would flicker in time with the stuttering noise that the pump was making.

Sorted that issue out with the rubber and its a LOT quieter, but it still makes a stuttering noise.. and my car still has an ignition cut issue which requires a dyno this week some time.