DDJ-SX2 sudden changes in output volume

Since a week I suddenly notice changes in the output volume from my DDJ-SX2. (Using the XLR to my Active speakers) The difference is quite disturbing, it is suddenly softer and then louder, and then softer again, with irregular intervals. All channels suffer from that. It doesn't matter what DJ software I use, I also have this problem when connecting a channel through a line-in. I noticed that the LED VU-Meters changes accordingly, And in order to correct the output level I have to use the TRIM knobs but when the output volume restores to the level I am used to, It is way too loud. I do not notice that when using the headphones, (no difference in the sound output to my headphones but at the same time there is a difference in the main output to my speakers)

I also tried this with the USB disconnected and only an iPad as input through the LINE IN connector, and it still happens. it drives me crazy.

Another weird thing I noticed is that when using Traktor Pro 2.11, I can see that when the controller is idle, on the screen, there are slight variances showing up for a second or two, under the different knobs (TRIM, HI, MID, LOW) like + 2.4 dB or -1.8 dB, completely random, and I don't touch the controller. 

What can be the cause of this ????? I am out of options in debugging.

It always worked fine, until a week ago ....