Fix Aesthetix Io volume control?

Try to remove knob and spray Caig De-oxit inside the volume pot. Spin back-fourth quick while you do that.
If does not help, open chassis and re-apply fresh solder(remove old one with solder removal pump) over the volume pot terminals. While you re-applying fresh solder on faulty volume pot you can do same on healthy preventative.
You will find plenty of youtubes on how to properly apply solder. Tools are best to purchase at partsexpress.com

Thanks, Czarivey. I will try your advice this weekend.

Get a new quality volume control (potentiometer) installed if it's not a bad solder joint.
The volume control even a quality one is the single worst component in an audio system.
It consists of a very thin spring loaded metallic (usually brass) wiper than has a very light pressure, point contact on a resistive track, either made from carbon or conductive plastic.
These are dissimilar materials as well, which is bad enough, and with a touch contact that the line level signal has to pass through. If the same contact was one of your RCA's or XRL's plugs you would throw it in the bin and get a new one. The same should be done with volume controls once they used too much.

They make "reasonable" contact when new but start to degrade from the first time they get rotated back and forth as the point contact starts to scratch and groove away at the soft resistive track, and wear starts from day 1 when new when it first gets rotated.

Cheers George