Perhaps the exhaust may run up the lines to the pump without air being driven TO the pump? Makes sense to me, but this is only a guess.
I think your popping is actually pretty normal, and probably nothing to be concerned about.
Maybe post a sound/video file to You Tube - (it can be pretty big), this way we can hear for ourselves for a better analysis for you.
3.4L, SC heads, 964 cams, B&B headers, K27 HF ZC turbo, Ruf IC. WUR & RPM switch, IA fuel head, Zork, G50/50 5 speed. 438 RWHP / 413 RWTQ -
"930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe
Movie: 930 on the dyno