If they are going to fix it under warranty let them go ahead and don't worry. However, I think it is probably not necessary but you don't need to tell them that.
I have had a TL2 in my home workshop for 4 years and when the machine has been idle for several days if it is run above 500 rpm it can make quite a lot of noise, especially if the shop has cooled down to about 10 C or lower.
Shortly after I bought the machine the technician from my Haas dealer came by and did a vibration analysis on the spindle bearings because they had received complaints about noisy machines. He wanted to use my machine as a comparison. At that time he told me his diagnosis was the grease draining to the bottom of a warm bearing and then needing to be re-distributed by running slowly before going to full speed. That sounded logical to me, more logical than a 'dry' bearing (how did it get dry I might ask?)
Rather than repeating myself an further I will refer you to these threads.
http://www.cnczone.com/forums/haas_l...y_spindle.html (TL-2 Noisy Spindle)