Link to a video on how to stop a chirping noise from your np231. One cause of chirping (there are probably many) can be that one of your bearings is spinning it’s outer race in the aluminum socket/seat. A lot of people will tell you you have to buy a new outer case. Not true. This fix has lasted 2 months with no sign of failing. Note: this video is really for novice diy people like me; I think a lot of people in this group are so accomplished at jeep mechanical fixes that they just need three words: Permatex sleeve retainer - replace the bearings and use this to keep them from spinning. For the rest of us, the how-to section starts at 6:30. The first part of the video is just my awful joking and dad sense of humor so skip it. I hope this helps someone. I didn't see anything like this posted here, but I may have missed it https://www.youtube.com/watch?v=FefYiGUwGSM