Loud humm when back out of the driveway

Does anyone know what is causing my humming noise that i have when im backing out of my driveway in the morning. Don't hear it the rest of the day. Just in the morning. Toyota can't seem to find it cause it doesn't make the sound when i take it to them. But its really loud and annoying and has been doing it since it was almost new. Oh and my a/c has a whistling sound in the fan. Anyone know what that is? Don't think its leaves or anything like that. Any help on either topic would be greatly appreciative thanks

 

same noise on my new o km Taco V6 TRD... also the sound is coming when rear wheels are spinning on snow..

 

Sounds like the anti-lock brake system doing a self test. Is the noise is coming from the passenger side firewall.

Blower motor squeek fix can be found here.

 

i have de same problem,exactly,maque a loud hummmming only when im backing up and only when the truck is cold,my truck is DC preruner short bed 2008,has been doing these for one year ,some times come to my main that the oil in the automatic transmicion has some thing to do whith these