All metal side panel reduces noise?

I got my 800D case yesterday and am pretty satisfied with it. I think a couple things should have been done better but by and large, it's a good case. One of the areas that I had expected would be better is fan noise. The 800D is much quieter than my older Silverstone TJ03 case but noisier than a Cooler Master ATCS 840 case with its 230mm fans that I have been using for two weeks. I wonder if one of the reasons for the greater fan noise from the 800D relative to the 840 case is because of the 800D's windowed side panel. Would swapping it out with the all-metal panel damp down noise in the real world, e.g. would any difference be noticeable? Or is the plastic window not much of a factor in fan noise?