Headphone / Left Fader Signal Issue

Hi - using traktor scratch 2
I get signal in the head phones even when both A+B buttons are turned off. The signal is louder when they are on
When the fader on channel A (left hand side) is up, i receive a faint signal in the headphones even when button A is turned off.
I've checked to see if my output monitors are set correct - they are
I've recalibrated my faders - it doesnt help
I've turned everything off and rebooted my computer 4 times - that doesn't work.
The only other things I can think of are cleaning that channel (if so, how should I do that? and what product to use?)
Should I install a TSP 2 update or
reset my unit back to factory settings.
I'm stumped to why this has just started happening, was fine the last time i used it (and havent changed any settings) and never had the problem before.
Any ideas, massively appreciated - thanks