New DDJ-1000 knobs "crakle"-feel problem

Hello,

I recently bought my first Pioneer piece of gear (DDJ-1000), transitioning from Serato and I like the experience. I`ve been very careful to check if everything works well on the unit, and I noticed something weird with some knobs from the mixer (Low,Mid,High): one knob, while i rotate it, at “9 o clock” I can feel like a “bump”, a “little jump”/crackly feel that happens. After a few days, the same thing happened with another 2 knobs. More peculiar is that if I don't leave the knobs at 12'o'clock, and I let them be for example at 9'o'clock, or 3'o'clock for a few hours, this "crackly" feel appears to other knobs also (I guess it starts happening to almost all the knobs) And to the knobs that were already having the little "crackly feel", it gets more, and "spreads" a bit to other areas of the movement also.

Also, I noticed from the beginning that when I was rotating some knobs, it was not a totally smooth feeling, it was some sort of .."sand" feel from the inside (very less but it was there). I thought maybe its very new and needs some "warm-up". 

On my other Roland controller the knobs from the mixer are working very smooth compared with this ddj-1000. 

I decided to go tomorrow at the store and exchange this controller unit. But still, I wanted to ask, if anyone had a similar experience with the knobs from a PIoneer unit? Is it "normal" with Pioneer gear?

After talking briefly with someone from the store, they pushed the "we will send the unit to the service and see if Pioneer decides to exchange the unit or not" card. But i dont think that is fair, right? I bought a new dj equipment and I want to exchange it with a properly working one. Not to send it to service and wait etc. The store has a 30 days returning policy which I'm counting on to just exchange my unit or just get a refund (if they still don't want to give me another one). 

A bit of unfortunate first-Pioneer-experience..