When using Spotify in my 2015 Subaru Outback, the volume randomly lowers then goes back to normal. Seems to last anywhere from 3 to 6 minutes. I do not believe it is a function of my speed (lowering when slowing down, etc.). The volume does not do this when I play through my Iphone or any other device - portable bluetooth speaker. It is only when I play through my car speakers. When speaking on the phone in the car the volume is fine. Just started happening about 3 months ago. Any help would be appreciated? Thanks.