I have an 09 Ultra Classic and the thumb volume switch seems to be acting up. From "0" bars to 1/2 volume everything seems to be OK. From 1/2 and up, there seems to be little change in loudness. It may be a little louder but no way full response to what my thumb is calling for. I have WO 575 bars with all wires running inside the bars. Any ideas on my problem or difficulty in fixing this problem?