I've found out yesterday that some of my speakers suddenly don't work, are these covered under warrenty?

 

As long as you're within your 4 year/50k mile Lexus Basic Warranty coverage...take it in to your nearest Lexus dealer.

 

Double checking the symptoms:
If you are streaming audio from your phone - is the USB cable touching the phone case?
Basic audio settings, fader or balance out of whack?
Homemade CD, plays properly in other devices?

"suddenly don't work" is a bit unusual, if they are blown out from a sharp transient pop or
overly loud passage they should sound muddy or fluffy but not out completely. Might you
have knocked wires loose in the trunk loading holiday gifts?

 

I'm using bluetooth most of the time so the cable shouldn't be an issue with it.

Everything is centered.

The backseat speakers don't have any sound coming out.