So I have a whistling/squeaking noise which starts at about 30 mph and the noise gets "faster" as I accelerate. It sounds like its coming front the passenger side wheel. I can only hear it with my windows down, when the windows are up I cant hear it. I dont think its the brake pad wear indicator because when I hit the brakes the sound is still there. The sound is constant whether or not I have my foot on the accelerator, and whether or not I am in drive or neutral. My truck is a 4wd 98 Sierra with the 305. Any help would be appreciated, its driving me crazy. Also, the noise is not dependent on RPM, so that kind of rules out the engine making the noise.