Bluetooth music gone a bit strange

[OriginalBigAl]

This is the first time its done it ,but today playing tracks off the phone via Bluetooth, the first 10 seconds of each track was really loud then quietened down to just below what I'd set then after another 10 seconds raised to the level I wanted. I can't think it was the car but I'm not sure , so I'm assuming it was the phone . I am using AIMP as a player but am not understanding some of its controls and parameters. What have I turned off/on to cause this. Normally use Android with the same player but today it did not want to connect, hence reverted to Bluetooth.