Rear differential fluid change, now grinding sound

[ntrail]

Hey guys... need some help here trying to figure out what is going on.

I have a 2007 2WD V6 4Runner, and today I changed the rear differential fluid to Mobil 1 synthetic. Afterwards, I went for a test drive and immediately heard a fairly loud grinding-like sound whenever I engage reverse or drive. It goes away after a second or so, so I think it is related to the transmission coupling, but I can't figure out what is going on....

Any ideas?

Thank you!

 

[ntrail]

Update: I just took it for a semi-extended trip around the block (up to 60 mph in the back area, ~10 miles), and couldn't hear anything of concern during the trip. About 90% done, I stopped in a parking lot to test if the sound was still there (going into drive or reverse, from anything else), and noticed it went away!

So with a hot engine, there aren't any sounds... I am going to give it some time to cool-off and check if it comes back with a cooled engine...

 

[ntrail]

Second Update: Tested it again this AM... very minor sound (beyond the normal transmission engagement I think) when going into reverse, and almost all gone when going into drive.

Any help or ideas on what might have happened / be happening?

Thinking back, I could of slightly rotated (very minor torque) on the driveshaft playing around under the car... but can't understand this. Also, at least some of the noise is coming from the rear brakes, when I switch from reverse to drive or back they seem to get pre-loaded and cause a bit of a squeak. I did use brake cleaner on them while I was under, but don't know how that would hurt anything there.

I also put just over 3.1 quarts into the rear differential, but maybe it wants even more (it was close to spilling out, but not quite)?...

Any help is much appreciated.

Thanks!

 

[JB.]

If you got 3.1 quarts in there, underfilled as an explanation is off the table.

I'd guess you're just hearing something you previously paid no attention to. When going into drive or reverse, sometimes there is mechanical noise, sometimes not.

If it's going to continue to bother you, you could do another drain and fill on the off chance the oil was contaminated.