Pulsating hums @ 70mph. Ideas??

[Dkon82]

I started to notice a hum that pulsates (about 2 hums per second) when going about 70. You can hear it between 65 and 75 but it's most noticeable at 70. I can't feel it I can only hear it; it's not that loud the radio has to be off to hear it. I heard it may be the diffs. I recently had my t-case services, I had them replace the oil with full synthetic (amsoil), they also replaced the rear diff fluid with the same oil. They said the front diff looked good so I guess I'll wait on that. They also greased all the zerks (non were dry).

Note:
Hum was noticed prior to t-case O ring repair (no issues there).
04 v8 100k.

Any insights and or ideas would be greatly appreciated. As always, thanks a million!!

 

[ClockWork]

I had a pulsating harmonic vibration from one of the diffs. Synthetic fluid solved it.

FWIW it was only noticeable when it was cold out. Perhaps it originates from the front diff.

 

[Dkon82]

Ya as soon as it started getting real cold is about the same time I started to hear the hum. I hope that's all it is. I'm going to do the front diff myself this week. Hopefully that solves it!
Thanks