Reply to Deck D volume fader acting weird

I don't know if it's broken but I was mixing and the volume for deck D stayed at around 50% and moving the fader did nothing.
I recalibrated the faders and played deck D again and it played at max volume (the fader was at max) but when I moved it slowly to 0% it 'lagged', stuttered about 4 times (e.g. 100-70-50-30-0) and finally got to 0% and now it's stuck there.
Should I try and blow dust out or is this another issue as everything else is fine on my S4.

OK it's definitely a dust problem because the fader was on max but no volume and when i blew hard the sound came on again, and now it's stuck on max. Now it seems to have 2 settings, ON or OFF. what the hell

I recalibrated again and it works fine. This is worrying though...