Sounds like it's not your gears.. are you sure the drive shaft is short enough now with the 8.25...?
Exactly what I was thinking. that why I asked about original axle. If I recall correctly, the nose on an 8 1/4 is longer than a 35, and so the driveshaft needs to be shortened.
Do you have an SYE in the back? If so, remove the rear driveshaft, and reinstall the front. See if the sound changes. Also, make sure the rear driveshaft slip joint isn't fully compressed, or dried out. Changing the normal length of the shaft because of the different axle, could cause binding in the slip joint.
David Bricker / SYR