Unwanted volume increase once Bluetooth is connected, only on rechargeables.

I have a problem with my Phonak rechargeable hearing aids that occur only when I pair my phone with them. After pairing (connecting) audio and calls, there is an increase in volume. When I exit the Bluetooth settings, the volume seems to normalize. This only happens with my rechargeable aids. I returned my old pair and got a new and improved pair called, Sphere. The problem is still present. I believe Phonak knows about this but plays like nothing is wrong. They want to put you through endless useless troubleshooting procedures, when the problem lies in their design.