Okay, I finally rigged the new Euro-Reef skimmer up so that bubbles aren't dumping everywhere in the main tank. It's getting adjusted, and seems to do a great job. Here's the dig: the vibration noise is unbearable! I can't even pinpoint it. If I turn off the pump to the skimmer, it stops. If I turn off the pump back to the main tank, it stops. Both run, it's a distractingly loud deep humming sound. Any ideas?

What pump are you using and how is it plumbed to the skimmer?

GenX-2400. It's assembled (plumbed in) directly from the manufacturer.

I have the ER RC-180 that has the GX-4100 on it for the re-circulating aspect. OMG the noise. Nothing would make it quiet. And like you, I couldn't figure out what was making the noise.... internal I guess... i don't know. You know what we did with it.... threw a bloody big towel over it. The weight made the pump vibrate less and the towel muffled what was remaining. Such a shame. It's such an awesome skimmer.

I just did a search on the GenX 2400 and the first page of links was all about noise. Looks like you may just have to get use to it.