Hi folks, have a recently rebuilt 455 in a 69 skylark. Stockish compression and heads from what I know. Stock manifolds, a TA-212 can, and power timed points style dist with pertronix and coil. Last week I installed a complete Holley Sniper EFI, with the tanks inc tank, walbro in tank pump, and associated lines and filters. It's been running incredibly well, but it's not a race car. It's my daily driver. It's mostly been part throttle with an occasional trip up to 4krpm, just letting the efi learn. A couple days ago, it started making a rattle around 1500 rpm with light throttle in gear, I backed off right away. In park, it revs cleanly and quietly. There is 1/2 tank of Chevron 92 octane in the tank. While poking around, I found a Burbley noise, the mechanical fuel pump with no lines is doing that, just pushing air. Block off plate on the way. The valvetrain appears solid, no bent pushrods or loose springs, etc. Any ideas? Sorry for the long rambling post, I tried to get as much info as possible. Could the mechanical fuel pump arm be bouncing off the cam, now that there is no load (fuel) to be pushed?