It won't matter how stunning you look in your new, trendy leather jacket if every time you move the material squeaks against itself. You'll be wearing the jacket for comfort as well as style, so you'll want your ears to be comfortable too, without worrying each time you move about the sound. You don't have to bring your jacket to professionals to solve this problem; you can fix that squeaking in your own home.
Wear the jacket as much as possible after purchase to break it in. Newer leather is more taut and firm; when it rubs against itself, it will fight the friction, causing the fabric to squeak. Many times a jacket needs to be worn and lived in to relax it. Move around a lot in your jacket while at home. Do tasks you would normally do, so that the areas of the jacket that will move against it the most will loosen slightly. Your jacket won't lose its shape, but it will squeak less. Wear the jacket regularly at home for at least a few weeks to see if it resolves itself without needing further treatment.
Dampen the jacket with water. Spritz a light mist of water on the jacket, then slip it on. Move your arms in circular motions. Stretch them behind your back and over your head. The slight spray of water will help the material give in to the loosening it would go through on its own, given time. Water may speed up the process a bit, but be careful not to use too much or your jacket will shrink. Never submerge your jacket in water.
Apply leather conditioner. Use paper towels to liberally dab the conditioner on trouble spots before going over the entire jacket with a light coat. The conditioner should sink in on its own. Leather has natural oils that need to be replenished now and again, or the material will become dry, squeak and may even crack. By softening the fabric with conditioner, you lessen the friction as you move, taking care of unwanted squeaks.
Don't use too much conditioner on your jacket or the article may become discolored. Leather has a natural capacity for the oil found in such conditioners, and exceeding that limit will darken the fabric where the oil collects.