Rear end noise

I have a 2007 4wd auto that produces a grinding sound from about 25 MPH up tp about 35-40 MPH.
I took it to a drive train mechanic who drove the car also heard the noise and indicated it sounded like the pinion bearing. This was a second opinion. Once up on the rack, he was unable to hear the noise. Pulled the inspection cover, oil was old but OK and no metal on the magnetized plug.
Checked the rear wheel bearings, no problem. Checked the front wheel bearings, both replaced, both warn....thought the noise may have been coming from there, transmitted to rear of car. Checked all breaks including e-break.....all looked fine.
To be on safe side, replaced front and rear diff. Oils.

On the ground, Car still makes the same noise. Tahoe from hell, any ideas?
Thanks, Dave

I have a 2007 4wd auto that produces a grinding sound from about 25 MPH up tp about 35-40 MPH.
I took it to a drive train mechanic who drove the car also heard the noise and indicated it sounded like the pinion bearing. This was a second opinion. Once up on the rack, he was unable to hear the noise. Pulled the inspection cover, oil was old but OK and no metal on the magnetized plug.
Checked the rear wheel bearings, no problem. Checked the front wheel bearings, both replaced, both warn....thought the noise may have been coming from there, transmitted to rear of car. Checked all breaks including e-break.....all looked fine.
To be on safe side, replaced front and rear diff. Oils.

On the ground, Car still makes the same noise. Tahoe from hell, any ideas?
Thanks, Dave

Did your mechanic use a stethoscope on the rear end when listening for the noise? Pinion bearings are pretty common on those and the bearings need to be inspected to see the wear. The rollers and the races will show pitting. Sometimes just the inner race will pit, sometimes both will.

Thanks for your reply.
Yes, according to my mechanic, they had sound devices placed "all over the car".
I would assume that the pinion bearing would make noise in the air (on the rack)?

I have a 2007 4wd auto that produces a grinding sound from about 25 MPH up tp about 35-40 MPH.
I took it to a drive train mechanic who drove the car also heard the noise and indicated it sounded like the pinion bearing. This was a second opinion. Once up on the rack, he was unable to hear the noise. Pulled the inspection cover, oil was old but OK and no metal on the magnetized plug.
Checked the rear wheel bearings, no problem. Checked the front wheel bearings, both replaced, both warn....thought the noise may have been coming from there, transmitted to rear of car. Checked all breaks including e-break.....all looked fine.
To be on safe side, replaced front and rear diff. Oils.

On the ground, Car still makes the same noise. Tahoe from hell, any ideas?
Thanks, Dave

if the sound is from a bearing I have had issues where the bearing and race look very good yet it still made a howl. you have to be very skillful to feel out a bearing with a bad spot on it.

front hub bearings are a well known failure item for sure . sometimes you just can't feel it so run it till it gets a little louder..

the grinding could also be the transfer case. check fluid for a blue color if black that could be the problem.

Thanks for the input. Oil in both cases was changed. I'm leaning more to the pinion bearing base on input from the forum.
DH