I have a 1999 GMC Sierra four-wheel-drive that has a howl in the front and that is most prevalent between 50 and 60 miles an hour. This first started four years ago and I had my mechanic replaced the front wheel bearing on the left-hand side and this seemed to solve the problem. Last winter I had him replace the axle seals in the front end and the howl returned. I recently asked him to see if he could figure out what was wrong and he suspected the pinion bearing and replaced it. This is only made matters worse and it is really bad when I'm in four-wheel-drive at highway speeds. Has anybody experienced a similar problem and found a solution for it. My mechanic is totally baffled
