Shorting plugs....

Chad:
My gear is all un-balanced so I cannot address your XLR question. However, below is a quote from member Nsgarch, which may still be buried somewhere in the archives:

"It is customary to short any unused RCA inputs on preamps. This prevents pops and clicks when switching your source selector between actual sources that are plugged in. Also prevents unused inputs picking up stray RFI. You can use pre-made shorting plugs or make them yourself. I don't recommend the Cardas caps because they don't actually short the input, but only shield the hot signal socket from RFI.

Unused XLR inputs do not require this treatment since they are balanced and self-cancel any noise."

OK thanks alot guys!

Seems like you got your answer, but I can confirm that covering the inputs and outputs makes a significant difference to the noise floor of my system. I'll have to test the comment about only RCA needing covers as I'm currently using covers for both RCA and XLR. As mentioned above, never use shorting plugs on outputs.

Hmnn, I've never had a "noise" or a humn from most of my system components over the years. Last year I upgraded to a matching Pass Labs amp/pre-amp and they come with shorting plugs on the balanced connectors. I don't hear any difference either with them in or out. that makes me wonder about Jeffcott's answer that XLR don't need them since they're balanced..., then why does Pass Labs, and probably other companies as well, bother putting them in their units? just curious.

With Pass Labs stuff you should use the balanced inputs/outputs when possible anyway.

I tried the shorting plugs on my preamps unused inputs and I really cant tell any difference.
But, what the hey, they are really inexpensive and I already had them.