Having 110db loss i wear naida in one ear (CI in other) the audi had maxed it out completely and said to me that it might give alot of feedbacks, they also gave me new mould which is arylic (sp) and quite stiff mold, I got constant feedback until i switched back to my old mold which is silicone and softer, I haven't had feed back since. I have now got small problem, the national health service had stopped making silicone molds because it's too expensive (sighs) I have told them that I am prepared to buy them myself. Sometimes we need to go the extra mile to get what we need.
Also hugging people is common problem, I have friends who are deaf and wears HAs. my CI is on my hugging side, I could hear their HA feeding back, it's just slight movement of the mold and HA.
The thickness of tubing is also a factor, the thicker of tube the less the sound escapes, every time i get new mold the tube were very soft and thin, i have bag of tubes at home which is thicker and more rigid but not hard.
Things you should look out for in the future, when the tube gets old it becomes hard, splits, there might be a hole in the middle (at the mouth of the outer mold) the colouring of tube (usually yellow) and the tube seperates from the mold quite often (they should not come out easily when new) this is when the tube needs replacing.