strange huming sound from ingine or transmicion

i need help,any time im going to back up most of the time when the truck is cold make a strong humming sound,2008 DC preruner V6 i'm wondering way,has been like that for 1 year now and is guering worst,it is only 40 K miles

 

If the sound is coming from the passenger side firewall, then it's the anti-lock brakes performing a self test. Perfectly normal.

 

It's probably just the truck warming up

 

Is it only in reverse your hearing this noise?? or if your trucks cold can you hear it when in park just sitting there??

Also, to make your searching easier its spelt *Engine and *Transmission (The search engine runs off direct spelling)

 

the noise is only when i put the transmicion in reverse and im moving,in reverse and not moving i don't hear any thing,thanks guys for you help, good bless i'll be specting mor imputs

 

Ho i'm forgot,thank you for correct my spelling,you know Inglish is my second languaje