yes, as mentioned, those water levels printed on the skimmer body are for the internal water level,
not the water level in your sump.
most sicce pump driven skimmers like about 7-9".
then the other thing you can do is cut the piece of plumbing on the return below the valve, so that the valve outlet sits below the water level in your sump and makes no noise...
like it is now, but it will be out of the water most likely if you lower the sump water level.