Humming Noise Rear End

[Explorin'VA]

I recently swapped a (disk brake, open) rearend from a 2000 explorer into my 94. The gears appeared to be in great shape (original factory parts). I filled the diff with 3 qts. of Royal Purple 75w140 w/ friction modifier. On the test drive I noticed a humming noise coming from the rear when I hit approx. 15mph or higher. It wasn't something I ever heard coming from my old drum rearend. I assumed it was due to bad bearings or a bent rotor backing plate rubbing somewhere. I was just going to fix it later.

I started reading about pinion angle and it made me wonder if mine is off balance. I eyeballed everything while putting the axle in, but everything is bolted to where it should be. The only suspension modification I've made is an extra leaf in each spring pack. Could I have thrown the pinion angle off while doing any of this?

Should I buy an angle finder to check if the pinion angle is correct? Or is it safe to just go ahead and do a bearing/brake job to get rid of the noise? Any advice is appreciated as always.

 

[PopRichie77]

A bad pinion angle causes the U joint to bind and jerk, vibrate, it doesn't hum. Humming usually means the gear set up is bad, mismatched gears or they are worn from lack of oil, unless worn very bad this is something you can't see. It could also be a bad bearing.