A few months ago this problem started, when I run water down the garbage disposal side of the sink and have the disposal on, water starts backing up in the other side sink. When I shut off the disposal power the water drains. The disposal is only about 3 years old. I cleaned all of the lines under the sink but could the drain be clogged once it goes into the wall and to the city sewer? Or is there something wrong with my garbage disposal drain? I looked inside the main disposal part (from sink)and removed the drain line leaving the disposal under the sink and didn't see anything clogged. It's like when the garbage disposal is running it don't want to drain correctly.