...transmission the car is awd.? I have replaced wheel bearings and the transmission and even rear wheel bearings and each time I do something the noise goes away and slowly gets loud within about a week, sometimes a few months and sometimes the noise starts back on my way home from the mechanic. Each time they think they got it and it seems like they do but it keeps coming back and its got everyone boggled. This is a 2006 chevy equinox. I even replaced the tires and still I have the noise. Car is quiet until I reach about 30 mph then a low hum starts and gets louder, at certain speeds it gets louder and others it gets quieter, sometimes going faster makes it quieter and sometimes it makes it louder. Any ideas?