So i am also experiencing this with my 2021 RTL. So i know its a BT issue / android auto issue. I only use Spotify for music and my issue is at low volumes below level 12. If I'm on Bluetooth i found that if i turn the phone BT to 65ish percent the issue is significantly reduced. I think its still there slightly, but it doesn't bother me unless I really pay attention to it. For android auto its a fixed volume that cannot be adjusted on the phone. I did however find a setting in the Spotify app called volume control and I put it on quiet. I haven't done enough testing, but I sat in my driveway after changing this setting and didn't notice a significant issue. I will continue to update as i play around with settings.