s10 1997 blazer sound when deaccelerating

[King of Kings]

I have 97 s10, 4x4 blazer. i have changed the rear wheel bearings, the vaccumm tube ontop of the transfercase, which was stuck, and both front wheel bearings, and vacuum switch under the battery. I have changed all these parts, which are Brand NEW. now, it used to be stuck on 4x4, but the change of the vacuum switch fixed that. anyway, there is a humming sound coming from the center front driver side (its really hard to pick point when ur inside the truck, driving). the sound only comes slowing, gradually, when you let go of the gas. If your driving about 30mph and let go of the gas, you can hear a humming sound, not soo loud like it used to before i have changed the hub bearings. if u press the gas pedal back again, the sound goes away.



Is it coming from the front differential? I can turn left/right whent when the sound comes, but there is no popping sound, so i know its not the front ball joints or stuff like that. what should I check? or should i just let it go until the sound gets worse and breaks down my truck.?? The rear gears have oil as well as the front gears. the sound is not soo loud, but u can hear it, sounding like if the rear gears were out of oil, but there're not. the sound comes somewhere from the front. Any suggestions??