I noticed today that the transmission makes a chirp sound when shifting from 2nd to 3rd and on occasion 1st to 2nd. The transmission feels normal and feels like it shifts well for an auto with 161K on it. I found a few threads where people were talking about it but no diagnosis and results.

Any ideas?

 

Without a video/audio I would only assume it is not the transmission, rather one or a combination of rubber things gone bad. These are all typical issues in need of repair: motor mounts, torque mount, tranny mount, lower control arms, and front strut top hats.

 

check them mounts

 

Most all of that is new. I did a search and found a lot of people with Nissans with the same complaint. Altimas, Sentras, i30/ Maximas. Most say it is the engagement of a clutch pack. I did a transmission drain and refill with some LubeGard additive-friction modifier. Has been quiet and smooth shifting so far.