2002, 2-Door, 4WD, Blazer 173k miles

Hey guys, got a new noise development with my Blazer. Been putting the regular highmiles on it again after a long peroid of working from home.

While at low speed I would hear a slight grinding noise from under my seat. This sound is most noctiable on a level grade, cruising at about 20 - 30 mph, with your foot ever so slightly on the pedal to maintain speed.
My guess is transmission or transfer case noises. It's not super loud, but I want to post about it anyway so that if it is part of a bigger problem getting ready to start, I want to know what I should do.

It has also been making an occilating droning noise while steering right.
For example: coming off a highway ramp, turning right towards a yield sign, at 35 mph, into a lane merge, you'll hear a droning sound from under the driver seat go whomp whomp whomp whomp whomp.
CV axle, front diff, transmission, transfer case? This is only while turning right. Turning left yields no noise that I can hear, and it only does this while slowing down.
This noise I'm more concerned about and may be tied to the other noise is does driving straight on a level grade at 25 mph with the throttle slightly down.

I should also mention that I have been feeling very subtle power surges duing accelration while turning right.
For example: turning right onto a round-about ramp to get onto the highway. After the apex of the ramp I begin to accelerate slowly still turning right, and I'll feel something in the drive train kick multiple times.
This is only while turning right. Turning left feels fine, and it only does this while accelerating.
Two things I've done that may be related to this could be changing the gear oil in the rear diff, or replacing the axle seal. I had a leaking axle seal on the rear passener axle that I just replaced recently.
Could the new seal be dragging on the axle while turning? Is it something in the diff I didn't put back right when unlocking the axle causing this?

During the time I've been working at home, I have still been driving it regularly. I took advantage of that time to follow my repair manual and do some much needed routine maintance.
One thing I did, that may be related to the problem was I change out all the gear oil.
I put Lucas 80w-90 oil in the front and rear diffs, and ACDelco AutoTrak II transfer case fluid in the transfer case. My manual pointed out that any 80w-90 gear oil will work, and that the transfer case specifically wants this AutoTrak II fluid.
I haven't changed the transmission fluid yet. That's on my todo list.
Other things I've done that may be related is that I've rebuilt the frontend suspension. Ball joints and all. I don't think that may be the issue, but I'm just pointing it out anyway.

 

This is quite odd. The issue may have something to do with body flex or noise transfer. I did have an issue with an F150 when I worked for Ford that had an issue where only on an incline and turning right it would start to go and then release and start to go again. Turned out his rear diff gear broke a tooth off. I’m not saying that happened to your vehicle but it wouldn’t be a bad thing to look into if possible. Also I wonder if when that body flex is produced when turning, if the steering shaft is touching the exhaust and noise transfer is causing it to sounds like it’s from under the seat. The exhaust itself could be flexing under your seat and rubbing on a driveshaft as well. That would probably be more due to a bad mount somewhere like on the engine or transmission allowing the exhaust or transmission to move just right. The only real thing I can think of at this very moment would be to lift the vehicle and place something under the right front tire and lower it back down with the wheel turned to simulate you turning. Then you can check to see if there is anything touching. This doesn’t always work but it doesn’t cost anything to try. Keep us updated and if I think of anything else I’ll let you know.

 

I say it's coming from under the driver seat because I hear it the most from the driver side window down. The sound could be from anywhere. I just haven't investigated the noise from the outside yet.
Rear diff is my main suspect right now because that's the last thing I touched before this started happening.
I had to remove the center retaining pin from the diff so that I could pull the axle out and replace the axle seal.
I'm hoping I put it all back together right. I spun it around a bit afterwards to make sure everything was solid before buttoning up the cover and filling in the oil.

 

That’s definitely something to check into. Once you investigate it further let us know.

 

Made a video showing the front diff and transfer case.
I think the groaning noise is coming from the front of the transfer case.
When I twist the front drive shaft, there is a clicking/clanking noise from the gears it sounds like.
When I spin the front drive shaft around, there is a grinding noise like a worn bearing.

https://www.dropbox.com/s/pkpnd8voci...47015.mp4?dl=0