my volume keeps changing while a song is playing

[pim2]

My volume keeps changing while I am playing a song offline I have it with every song even the songs I downloaded before this problem appeared. I've tried deleting the app and downloading it again and downloading all the songs over again but it didn't work. I also tried different headphones buy it keeps changing no matter where I connect it to. Does someone know how I can solve this. (I've got a Samsung galaxy S6)