There is going to be a lot of chasing in this diagnosis, but keep tabs and it will work out. It is possible that one the speakers has become partially lose form its' mount, then it resonates against the interior.
There are several modes for each pitch of resonant frequency.
Meaning the loudest will be slowest as it has the greater magnitude and they get higher in pitch as you speed up. So, there
are many suspect areas to look at.
Is the left front the only speaker in question? How many speakers does your truck have? Do you have an amplifier?
Inspect the speaker/s that you suspect and see if they are mounted tightly.
If this does not fix it, they are plenty of things to consider and then attack it by process of elimination. Body and suspension noises are hard to nail down.
If you had a warped rotator you would feel the pulsing in the brake pedal.
It could have a rock or maybe the wrong bolt was used to mount the caliper and it is rubbing the surface of the rotor because it is too long.
I will research/put some thought into it and get back with you tomorrow.
Saturday, August 27th, 2011 AT 3:53 AM