Musical distortion with S11

For about a month now, I've been using Starkey S 11 aids. I've been bacl to the AUDI twice to get the aids adjusted. The trouble I've been having has been distortion/vibration in high frequencies. So far he has not been able to stop the problem and seems perplexed (a little discouraging). The distortion seems to happen mostly with mid to upper ranges in the Saxaphone/Clarinet and occurs when the notes are held for a second or more. I do not notice it in speach. Is this something that is fairly common? Any suggestions for waht could be explored to fix it?