I'm getting ONE loud knock out of my NDS crank arm upon take off from a stand or whenever applying full force rotating forward immediately after applying resistance/backforce. It happens once, usually only if I apply full force or weight and then goes away on normal cadence. I'm also getting some mild creakiness when applying significant backforce coming down hills or slowing down quickly. My buddy at my LBS thought it might be my BB spindle needing a clean/regrease. Did that and still happening. I'm thinking it might be the pedal(s) needing the same treatment. Your thoughts?

SRAM 300 w/gxp if that helps/matters. Thanks in advance.