Water is sitting in both kitchen sink drains with equal pressure. When running dishwasher it bubbles up some on both sides. When running disposal, water sucks down on disposal side, but then creeps back up after shutting off. Each sink is plumbed with its own drain line out and I have an air gap with drain line from disposal going to one side and drain line from dishwasher going to other side of air gap. Need help. I checked traps and they are clear. Also when I run the dishwasher and also run the disposal, the water drains in both sinks just fine and no back-up.
What is the problem, and how can I fix it? Is this something that I will be able to easily repair myself, or do I have to call a professional plumber?