Bed sounds like a washing machine on spin cycle when going > 60MPH

I've had my 09' Taco for a little more than two months and notice that when I'm on the freeway I can hear this faint "machine gun" or "washing machine on spin cycle" noise coming from the back. The bed doesn't appear to be vibrating and there is no driving problems. Is this normal because there is no metal frame under the truck bed? It's completely under warranty, but I thought I'd check here first before the service mechanics think I'm just a silly girl

 

you cant feel anything,you just hear it?

 

1st, Check to see if your spare tire is tight in the holder. Ive had more customer comebacks for noises and the spare being loose. Good Luck

 

air pressure in tires maybe?

 

yea, it's just the noise...it gets louder when I'm up against a concrete divider or a car passes...it's annoying when all the windows are down.

 

Coolidge...thanks...I'll check it.

 

what do the tires look like.are they feathered on the edges?