Odd Sound While Driving

[pinksoviet]

Greetings! I recently acquired four new tires (Bridgestone Alenza's) and ever since I have been hearing an audible noise whenever I'm driving over roughly thirty miles per hour (interestingly enough, the sound in question dies out past fifty miles per hour, though I'm to believe it is because other road noise just overpowers it).

The sound itself is a sort of low warbling emanating from roughly the front portion of the car. I suppose another way to put it is like the sound of distant helicopter rotor blades slowed down (such as in those war movies). Sorry if this doesn't seem all too clear. Anyways, there isn't any vibration in the car itself nor in the steering wheel. I did go back to the shop that balanced my tires and they assured me that they balanced the tires properly (it's a Firestone center). Also, I did get an alignment shortly afterwards, and the sound is still there.

It would be greatly appreciated if anybody could shed some light onto the cause of this sound. Could it just be that the tires are notorious for creating road noise, or perhaps a more grave underlying problem? Many thanks in advance!