Hi have started to get a problem with my UR-22C. I use it only for my guitar, and started to get a crackling noice when using the HI-Z and playing.
The humm is always there and increases if i have higher gain. And when playing a note it fizzes and its mostly hearable at the end of the note.
WHen switching off the HI-z it sounds good.
What can be the problem? And how do i solve it 
Is your input signal to hot? Should be around -12 to - 6 max showing in your DAW. Also using a high gain plug-in will generate noise. 
Are you using any of the Guitar sims? Those notoriously break up with any input over -18 or so (even the Clean with all settings dry). Its so bad I though mine was defective. I had Yamaha support on the line and when they tried a guitar at their end, and heard just how sensotive those sims are, he was like “wow!” Lol
Problem solved, then? 
When using Hi-Z, don’t add any Gain…leave it at zero.