Covers on unused RCA inputs?


Years ago, I vaguely remember being advised to put little plastic covers on the unused RCA inputs on the back on my preamp. These plastic plugs had a piece of metal that connected the two poles of the RCA input. The theory was, by bridging the two sides of the RCA input, ambient RFI and static electricity were blocked from entering the preamp, resulting in a lower noise floor.

Of course, these plugs could only be used on RCA inputs, not outputs, as this would short circuit and possibly damage the preamp.

Has anyone heard of these gadgets? Does anyone use them currently? Thank you.
javachip
I use them on my unused phono input (no turntable presently) to ensure I don't accidentally plug a line level device in there.
I used Cardas RCA caps and there are no audible effects. Scratches on the input rca jacks, but less dust, is about all these things were able to achieve in my system.

And what is it with the bleeding of signal from other sources? I've seen so many preamps having this issue. Is this a common preamplifier design flaw? Is this an indication of something going wrong?
Audphile1...The good old fashoned rotary selector switch used to have a "deck" the function of which was to short out all the inputs except the one selected. We no longer see rotary selector switches, and the solid state circuitry common today runs at much lower impedance than old tube circuitry and is less susceptable to bleed through. So, preamp designers don't bother with shorting the unused inputs. I guess you could call it "a common preamplifier design flaw". Gone, like tone controls and Loudness compensation.