I too having this issue, not with car audio but with a home audio set up i have
For a good while now I have been having this issue where I would be listening to music via Bluetooth and it would randomly change to another function like CD/Radio/aux etc. This happens everytime volume is above 65% as you stated
And I don't know why it is doing this
So was the issue fixed by checking and fixing the ground connection??
If so that might be my issue as well...please let me know