Its hard to say without actually seeing the tires, but its possible that they are correct about your tires causing the noise. They may be referring to "heel toe wear". If it is, you can feel it by running your hand across the outside tread blocks. It will feel rough going one way and smooth going the other because the trailing edge of the tread block will be worn down more than the leading edge.
I have found that even if aligned "correctly" (some toe in as to specs) the e90 will do this to the outside edge of the front tires eventually. Its worse on some tire designs than others. It also makes more noise on some tire designs than others.
If you don't have a suspension problem and your car is aligned correctly, you can try to counteract this by rotating the tires. If you have a staggered setup rotate side to side, if you have a square setup do the normal cross rotation. The goal is to get the tires to switch rotating direction.
Last edited by asus389; 01-20-2013 at 10:37 PM.