Flower, I just want to say I love these In The Moment stream of consciousness diatribes you sometimes post!
Though I'm sorry you were in a pissy mood about the whistle, I'm glad you found out what it was. Was this your Tunze nano skimmer? Mine's never made that noise.....strange. But I know the feeling about noises you just CAN'T PINPOINT NO MATTER WHAT. At least you're not going to be sleeping to that sound tonight.
I just want to point out one thing....you're still in that New Tank stage here. You're BOUND to get at least a little cyano until your tank balances. I've never had a tank that didn't go through at least a brief cyano stage during the initial few months. I think you should get the extra powerhead...you're the best judge of your own flow... but I certainly don't think it's cause to hang your head in defeat.
Now as for your sump. Chaeto is your friend. A hunk of Chaeto, combined with a 5 dollar shop clamp reflector and a 65 kelvin swirly bulb, will help your pod population and your filtration tremendously. It should also help manage the nutrients and keep them locked away so you'll have less cyano. But you already know this. I'm just reminding you because I'm sure the whistle is making you forgetful.