Martin, when I first got my mcp355, I was impressed by how relatively quiet it was, at least in comparison to the pair of ddc-2's that I have.

However placing a load on it, definitely increased the level of noise, and dampening the sound works great if you do it completely. The other option that works not quite as well is to suspend it. In my case, it's hanging via tubing from my res.

I'm still not happy with the noise, but it's tolerable.