Rates sound about right. For myself i find that for high rates about 50-60 degrees on elev and rudder and 40 on aileron sufficient. Im using 80% expo at high rate. Ive heard this is what the boy uses too.

The JR digis make that sound because of the load of the control surface weight on them. Id only start worrying if they went quiet. Sometimes you also can get them oscillating in the pits if you go to full deflection and let the stick go so it vibrates around center - i think the servo picks this up and tries to follow it, certainly havent had any problems in the air.

I'd start off with the C of G in recommended position and then gradually move it back, slightly increasing the amount of expo on the elevator if you need too.