External noise gate pedals don't work with the Catalyst on high gain?

[AGXNY0000]

So I have a Catalyst 100 that I'm playing on the Hi Gain channel with, so naturally, I need a noise gate.  I have my Pod Go setup in the Catalyst's FX Loop, and I tried using the noise gate in the Pod Go both before and after the Catalyst's pre amp.  I can turn both gates all the way up and it brutally sucks my tone, but does absolutely nothing for the unbearably loud hissing.  I also tried using my boss NS-2 noise suppressor.  I tried it before the pre amp and in the fx loop.  I also tried both of these with and without the 4 cable method.  It does nothing at all, even on the max setting.  When I use the built in noise gate on the catalyst it gives me complete silence, so obviously I'll just use that for now but I'm just wondering why is the built in noise gate the only one that works?

[rd2rk]

IDK, but I suspect it's before the preamp.

I use my Cat100 in 4cm with my Helix Floor.

Using either the Helix Input NG or a NG before the FX Loop works fine.

After the FX Loop has no effect.