Contradica,
I have also experienced the twitch but it was a neck muscle. I told my Audi and she turned the volume down so I was not getting hit with so much current. This high current also makes the batteries last a much shorter amount of time. The speed at which the CI hits the nerves also plays a major part in how long the batteries last.
I also twitch a little when I touch the electrical plug in the wall. A CI is no different. It sends electrical current to the nerve. If the amperage is to high (very high volume), you may feel it in the way of a twitch. If I can remember correctly, mine centered around electrode 19 and 17. We turned down the max output on those two electrode but also lowered 21, 20, 18, 16 and 15 so the sounds still sounded right. After the C and T levels were programmed, the Audi turned down the max output again.
Noises sound normal to me and I like it. I currently run 1800/sec but have a 3500/sec if I want to use it or per say re-train myself to hear. When I was learning to use the CI, I used 3500/sec most of the time as I found it easier to learn how to hear again.
Steve