MK6 Golf speakers not working properly

[Baggies93]

Hi guys

The speakers in my MK6 golf aren't working properly. They either sound very distorted or complete flat and tinny - as if the music were playing off a mobile phone loudspeaker. Weirdly, when all my windows are up the sound is completely tinny, however, when I lower one slightly, the sound then becomes very distorted. Either way my speakers aren't functioning properly. They are completely standard.

Anyone know what this could be or how I could check this? I've tried different sources i.e Aux, radio, bluetooth and the problem persists

Thanks!