I actually found a way to fix front speaker distortion without root.
1) Disable Google's MusixFx App (com.android.musicfx)
2) Install an equalizer app (In my case i used Equalizer FX. Pro Free version)
3) Open the app (if you haven't disabled yet Google's MusicFx app, it will told you to do so)
4) Depending on how is affected your speaker because the bad mounting (Google's fault) you will have to play lowering the frequencies. In my case I only needed to lower 910Hz to -7db
5) No more distortion!!!....
The only down side it's that you will get a less louder speaker, but 100% enjoyable sound!
I had to return 4 devices until I decided to find a way to "fix it" without rooting... I think Google was already trying to fix it because MusicFX app was updated in latest February update. Let's see if they officially release a fix. I think I will ask for RMA again anyway...