I'm running a waveline 5500 and the Jebao 12000 on different tanks and the 12000 is just as quiet, nearly silent with a faint whine from close up. The air intake on my skimmer makes more noise than the return pump does, and my MP40's do too.
The one thing I wonder is how everyone plumbed it in as far as plumbing diameter goes, and total pump head. I do know that increased pump head can cause a change in noise level from pumps, so that could be an issue. I used 1 1/4" PVC to a manifold feeding returns and reactors. The dual returns from the manifold are 1" so I expect that I don't have a lot of restriction in the return system. I didn't do the math and I'm aware that too large of return pipe can add to pump head, this just seemed reasonable from past experiance.
I'd be curius to hear from others as to how they plumbed their pump and the noise level they have.