When cold or just starting up, there are no problems…..that is, all engine and transmission sounds are normal. However, when things get warmed up and hot there is a distinct vibration or soft rattle from the middle to rear of the car when the speed is around 10 miles per hour…..and when going faster, the sound goes away (probably drowned out by increased engine rpm and air vent fans etc,). So when the speed is reduced this sound can be reproduced at around 10 mph every time and it is somewhat louder if going up hill. It sounds like something is rattling (very subtle sound) but never at all speeds above 10 mph. Any ideas ??

 

Could it be your differential? Mine would make a vibration that felt like I was going over the rippled pavement that they put on the sides of the road to keep people awake when I was turning at slow speeds and I never noticed it at higher speeds. Required a new diff. A few others have suffered the same fate. Good thing you have the warranty if it is.

 

Differential input shaft or bearing will vibrate when not under load (coasting, slowing down gently) but under load it goes away because the torque will push it against the side of the case. Should be fixable but not easily.

 

I did drain the diff fluid as much as possible and refilled with new (75W-140) but could only exchange around a quart (it holds 1.3 qts) but this did not change a thing. Oh and the magnetic plug was really packed with gunk.

 

Diff magnetic plugged packed with metal is not good.