The ReSound Smart Fit fitting software has a feedback test that is run independently on each ear to evaluate the potential for feedback. It’s supposed to be run after any serious fitting change or with a new pair of HA’s, etc. You might recognize when it’s going to be run as your audi might advise you that she’s going to play a test noise and then you’ll hear a loud test buzz played in each ear. The program is playing a frequency spectrum into each ear with your receivers and molds or domes in place and then effectively having the external mics listen for what sound of what frequency is leaking out of your ears to the mics. The fitting program effectively records this profile and should adjust the allowed gain to reduce it below the level that the test results indicate would allow feedback. The audi has the option, as Raudrive indicated, to go beyond what the program decides and reduce gain as advisable in individual frequency channels even further.
The descending gray areas show the potential for feedback for me with an open fit (graph on left) and a very closed fit (graph on right) in the following post. Self Fitting Resound Quattro 9s - #2 by jim_lewis The top red area in each graph is the amplification region that’s beyond the capacity of my MP receiver. The amount of amplification involved changes according to the program in use so in your case, you might be interested in having your audi show you what the potential feedback areas are relative to the gain applied for soft, medium, and loud sounds when you’re in the Music program, which I think is where you said you experienced the problem.
You can see for me how wearing a closed fit, by reducing the potential for feedback, has given me a lot more amplification headroom to use an experience profile and a fitting algorithm that allows me a lot more amplification (the better to hear you with!) than possible with the new user reduced gain profile and fitting algorithm shown on the left when the open fit I have there allows the potential for lots of feedback if I have much more amplification than the restrained “intro” settings are allowing me.