I would check your belt but I have heard lots of CTDs chirp on shut down. The motor is coming to a stop really quickly and with the momentum all the accessories, the belt can chirp. With the 4wd thing, have you tried rocking the wheel or even backing up if it gets stuck? When I first started using my 4wd, I noticed every once in a while, it would stay in 4wd when it said it was in 2wd but after rocking the wheel while driving, it took that little bit of tension off the TC and would unlock. Doesnt do it anymore though.