I hear a type of humming sound, think it is the tires, have checked wheel bearing and they appear fine, sounds almost like rocks in the tread , but a little lower pitched, the tread is still ok, is it just tire wear...the sound goes up and down with speed.Is this just normal ? Any suggestions?

 

Check tire pressure. Then check for abnormal tire wear. Could be an alignment problem. Lastly, make sure that tires are rotating in the right direction if they are uni-directional.