6 m/o puppy afraid to go outside

This is my first dog, and he’s crate trained and are now working on potty training. He hasn’t had an accident in a few weeks, but everytime I grab the leash to take him outside- he runs to his crate and starts shaking. He refuses to take treats outside and will only take them after he gets back in. While walking outside, his tail is tucked, and every noise freaks him out and he runs backwards. Any advice?