sudden bad sound on macbook pro 2012, Yosemite

Hi guys,

I've got a macbook pro 13" from medio 2012, 2.5 Ghz running Yosemite (10.10.2). The other day it suddenly played back with an awful sound quality, overall scratchy and unclear, and with a noisy dominant bass. It appeared to play back with the same quality in headphones as well, also after relaunch. It persists in all applications including iTunes, Spotify and DVD-player, though not when playing videos on e.g. youtube or facebook.

I've tried deleting all files from /library/preferences/audio, typed the "sudo killall coreaudiod" in Terminal and reset PRAM without luck.

I guess it's a general software problem but I'm not really sure what to do. I can't find any useful answers when searching it up; other people are having audio problems after updating to Yosemite but not similar...