Sound distortion from the speakers on MacBook Pro (Retina Late 2012)

So I have this MacBook Pro for about 2 years and it seems that both of the internal speakers are providing distortion to the point that I can't even use them anymore I have to use the equalizer to turn the bass all down so that I can hear it a little.

I read a comment somewhere that they can be fixed without needing to replace them. I wanna know if there is the guide or a way which I can follow to try to get them fixed without needing for expensive replacement as it seems that both of the speakers required replaced or fix.