It could. There are things you can do to quiet it. I secured some filter floss just under the inside of my overflow to reduce the flow noise. Over time it will develop a build up that will quiet things down, also.
Just thinking about it, and I missed the obvious. You could increase the amount that trickles into the emergency drain instead of lowering it. This would be the easy answer. Set your MP40 to max flow, adjust your valve, and when your MP40 slows down it should increase the flow through the emergency drain without dropping level.