Thank you fellas for your suggestions.
Unfortunately, sanding will not solve the problem. I just right now disassembled the simple button array behind the front panel and discovered where the source of both the button sticking and the grating sound originates.
Smoothly melded to the back of each squat fat cylindrical button head is a long thin cylinder that reaches past the ~1inch depth of the front panel and pushes a small button on a circuit board on the main chassis which houses the actual components that translate the physical act of button pushing into electrical signal.
pic of circuit board
the click-action of the buttons on this circuit board is splashy soft--the kind I would like to have on the aluminum button array attached to the front panel.
At any rate, even as I thought that the grating and the sticking could be coming from the squat cylinder of the button head rubbing against the short wall of the well in the front panel that embeds this part of the button, I also could tell this was unlikely because the diameter of the well wall is significantly longer than the diameter of the squat cylinder such that the cylinder does not always brush up against the wall when it gets stuck.
Now that I have disassembled the button array, I can now see that the grating comes rather from deeper in the array--between the long thin cylindrical part behind the buttonhead and a very thin aluminum tunnel, or tube, which guides the thin cylinder towards the proper button on the circuit board. If I may be crude: basically, the problem is that the guy part--the finger behind the buttonhead--copulating with the girl part--the tunnel--is having difficulties because the girl part is not properly "lubricated"--that is, there is too much friction between the inner wall of the tunnel and the long thin cylinder that vascillates inside.
The inside of this thin tube would be difficult to sand because the inner diameter is roughly 2mm long. Moreover, subtracting the inner diameter of this tunnel from the outer leaves me with a tiny number.
Rather, what this tunnel needs is some sort of non-degrading coating which lowers the friction of the plunger action inside this tunnel without leaving residue. But I don't know anything about such coating or how to apply it in such a narrow tunnel.
I will instead try to see if a small rolled up piece of notebook paper can be finessed inside this tunnel and successfully lower the friction.
I will write back with my results shortly.