Well, unfortunately the sound is back. The sound is still coming from the front of the tractor, however it is making the noise in 4WD and 2WD now and most notably in reverse. I am going to remove the 4WD driveshaft and try driving it around to see if the noise is still there. Not sure if I mentioned it in a previous post, but the owner that I bought the tractor from had the clutch replaced... Could there be anything in the clutch that could be out of adjustment that might be making the "howling" sound that I am experiencing.