Nob turning = static

[リチャード]

So, this problem first arose about two years ago when I had owned my Astro A40's for a little more than 3 years already, and turning the nob to raise or decrease the volume would, instead of changing the volume, just produce a bunch of static, until I had turned it far enough to change the volume instead, that was on the mix-amp that comes with the Astro line-up. That headset finally broke a few weeks ago and I am replacing it with the HD559, since I don't play on an xbox anymore.

 

Anyway, now I encounter the same issue again, except this time on my speakers, Logitech Z623--Turning the volume nob produces static instead of changing the volume. These I have only owned for two years, and I haven't used them for a year due to living abroad.

 

What is this? Can I fix it? Can I prevent it from happening in the future? Thanks!