The problem is endemic to 1st generation Volts and other GM vehicles of similar vintage. For a detailed analysis, look at this post, and explore its thread:Hey everyone! I listen to a lot of piano music and have noticed that it sounds so flat on my Bluetooth! I'll try USB and AUX to see if that helps at all, but has anyone else noticed the music sounding flat?
It sounds great on every other car I do Bluetooth on but on my 2015 Volt it's maybe half a note flat.