Cardas Machined RCA Caps.???

Yes, but you must cover all unused jacks to realize the difference. I mentioned in an earlier thread that I covered all unused jacks in my system for several weeks. I then removed them all and noticed that they did indeed lower the noise floor. I have since put them all back on, and I have also covered my unused XLR openings with Cardas XLR caps.

I use them, but I haven't really identified an audible difference. I live in an area where there isn't a lot of steady electromagnetic noise. Perhaps there is an audible improvement when a noise source comes close (e.g., electrically noisy diesel motor).

I understand the principle of better shielding, and I believe it is desireable. I believe my system can sound audibly better based on the cumulative benefit of a number of individually inaudible improvements, and this could be one such.