I recently purchased a 2017 MKZ with the Ultima system and so far, I've brought the car in because of excessive vibration/rattling in the doors. I purchased an app for my phone that will play all the Hz's of bass and treble so I could trouble shoot what exactly is going on and not have to wait for that certain part of the song that makes the noise. Upon further inspection, I noticed the rear door lowest speakers (there are three) on both sides aren't emitting any sound. They should be just as loud as the front door speakers am I correct? The fader is in the middle position too. Could someone with this same system check theirs just so I know what is correct?