Bad radio control knob?

Hello again,

So this 2009 GLS was purchased used 3 weeks ago. I already posted one problem but another came up today. My radio control knob (right one), all of a sudden, do not move smoothly...well i should say it did but hen it didn't, like broken glass or sand was behind the knob, but then it moved smoothly again.

Out of warranty and not interested in replacing the head unit but was wondering if the knobs could be removed.

Thanks again!