I went out and started my truck tonight. The temp outside is 28 degrees. The truck was plugged in and had been all day. I started my truck and was sitting in it waiting for it to warm up. I usually wait 5 min. I had the heater on high and turned to the defrost/floor mode. All of a sudden a loud humming sound started from behind the dash. The sound goes away when I turn the blower to off, but comes right back when I turn it on. My heat in the truck is working just fine. I tried all the different position selections for the vent and they all seem to be working except when I turn the selector to the defroster mode. It takes about 10 to 15 seconds to work. I am aware of the TSB on one of the door hinges in the vent system not working. I'm wondering if it could be that or possibly my blower motor. My family is going to Kansas City in the morning. Do you think it is safe to go or am I in danger of losing my blower motor?