04 Trailblazer Jumps in Auto 4x4!

Hello,
I’m writing this because just this past winter, I noticed I had a ‘ringing noise’ in my front end while I’m 4HI (I might only use 4x4 once a year). This past week, I cleaned my truck and accidentally flipped the switch to auto 4wheel. Half way down the road, felt like my tires were loose. Checked them, all tight. Seemed to go away long enough to get home. Next day I drove it again (in auto 4x4 because I didn’t know it was on and it’s also the summer months over here). Anyways next day, feels like the brakes kept being applied every 3 or so seconds. Every 3 seconds I felt a loud bang and my truck would jump. During this time, I was unable to go over 15 mph and heard a loud ringing again in the front end. This is when I thought that it sounded like the 4wheel LO was on. That’s when I checked the switch (which was on auto 4x4)… I’m assuming it’s my front differential since I have NO noise in my rear end. Also in 2nd it’s smooth as butter. Just curious if a Chevy tech may know possible issues before I go into shop.. thanks!