The heater blower in my 08 Sierra 5.3 makes a high pitched noise from under the dash on the passenger side. It may come at will in speeds 2 to 4 but will go away in 1 or 5. It seems more like a vibration than bearing noise, but I can't detect. Sometimes going over a bump will make it start or stop, but the fan also makes noise when the truck is parked with the motor off. Everything works, but it is annoying. Has anyone had a similar problem? I don't want to tear apart everything and still not find it.