The noise kit shown above arrived today, and I had time before heading off to tonight's pistol match to try some of it out. The kit has more items than I need at the moment, so I only installed the coax noise filter (the box) and the DC ring filter.
Being a newbie, I know very little about noise and what qualifies as "normal", so I decided to take a photo of the spectrum scope "waterfall" before and after installing the filters. As you can see from the clock on the screen there was about 6 minutes between the two pictures, and the band may have changed, I don't know, but in looking at the before and after, the after shot seems to show slightly less noise. Will this be enough of a difference to matter to me? Not sure. I should have taken audio recordings to compare, I guess, but I didn't think of it.
Before:
After: