Last night I turned on the unit in order to try the suggestions that were made to solve this popping sound issue.
Guess what, no sound......aaaargh!
I turned the unit off, waited for 15 min and turned it on again, still nothing, I did notice that the tuner received a signal.
Everything looked normal, the lights were on (but nobodies home ;-)), I could change settings, change rigs, add eq, stomp boxes etc, but no sound.
Tried the alternative input on the back and changed guitar cables & switched guitars, but still nothing.
At this point I started to get visions of myself in the attic looking for my UX2.
After repeating this process of turning the unit on & off 4 times, It started producing sound again.
The sound however wasn't as good as usual and also seemed lower in volume, I always have my master volume on 0.1 and rig volume on 50%, amp & cabinet volume both on 0. With these settings the unit did not produce any sound, I had to increase the master volume to 0.4 in order to got some sound out of it, all other settings stayed the same. With the master volume set on 0.4 it still had a lower volume than it had before on 0.1?
I decided to repeat the process of turning the unit off and on again, but after doing this 3 times, sound quality nor volume improved.
I decided to do a factory reset, after doing this, the sound quality & volume was back to normal level.
I lowered the clean sense to minus 5, checked the cab & amp volume which both were on zero and played my Angel of Death/Reign in blood/Dead skin mask medley for a couple of minutes to check if I would have these loud pops again and to get rid of some build up frustration/aggression...
I didn't have any loud pops, but I only played for about 10 minutes since it was already late & I had to get up early to go to work the next day.
So it might be a bit early to say the problem is solved, after the weekend I will report back again.