To answer your question, the first thing I would try in that situation would be custom earmolds. I know that seems like it would defeat the purpose of open fit hearing aids, but there are very small molds they make now, with a very large air vent to keep the open feeling and benefits. The reason the may help with the feedback on your hearing aid is that it would direct the sound in the right direction.

There are two major bends in the ear canal, each going a different direction. When the open fit tubing isn’t pointed correctly in the canal it may cause the sound to bounce off one of those bends, back out of the ear and to the microphone, causing feedback.

What the custom earmold would do is make sure that the sound waves are headed in the right direction.

I’m assuming your local Siemens dealer already tried the typical diagnosis routines, such as checking the physical integrity of the tubes (no holes or cracks), and running the feedback calibration in the hearing aid programming software. Which if so, I would say trying a custom mold would be your best bet.

Here is a picture of custom open fit earmolds taken from http://www.greatlakesearmold.com/open_fit.asp:

Another site where you can get a good idea of what the custom molds are like is:
http://www.microsonic-inc.com/index2.php?section=46

If you want to give it a try you should see your dealer and ask him to take impressions of your ears for custom, open fit molds. Then they will send the molds to the lab they use, and have you come back in to try them out when they’re ready.

Let me know if you decide to try it out, and how it works out. I’ll get back to you quickly this time!