Maybe you're missing some filtration before skimmer? Mine is dead silent and I see no noticeable detritus on/in it other than the crap in the cup.Just giving my 2cts here:
I got the 600i for my tank when i started a year ago, i ran it for 2 months and then decided to swap it out for an ARKA Core. The difference in sound is HUGE. The deltec was the loudest thing in my system, now i barely hear anything when the cabinet is closed.
Another downside for the deltec: it needs a lot of cleaning to keep it running efficient.
The plates in the bottom that pass the water to the outlet tube get clogged easily with detritus. They require complete disassembly of the the skimmer to clean them.
Even when cleaning is needed, it is simply a few thump screws to take everything a part. Even the pipes are easily removed.

