The dolphin pumps are probably the second quietest pumps available for this app. The quietest (by both technical info and my own experience) are the CustomSealife T3 and T4 Titanium pumps. Incredible 30db of noise at 3 feet. Even with my ear right next to it I would have problems determining if it was running. I used a T4 on my sump at one point for my 125 - only swithced recently when I went with OceanClears on my 125. The one big problem with the Customsealife pumps and also the MAG pumps which I did not mention earlier - no good water isolation from magnetic coils from a heat transfer point of view. All other pumps I mentioned have excellent thermal isolation (particularly the Blue Line, Iwaki, and Dolphin). You naturally want this and the Mag 7 will undoubtly raise your tank temp at least 2-5 degrees from ambient temp.
another important consideration is effeciency - watts/GPH
- i.e. paying a little more for a better pump can save a lot in the log run. For example a pump which costs $50 dollars less but pumps the same water volume but uses 100 watts more to do it may result in an additional cost as follows:
100 watts x 24hrs per day = 2400 watts/hr/day or 2.4 Kwh(kilowatthours per day).
assuming $.15 per Kwh (check local area for exact costs) then:
2.4 * .15 = $.36 per day * 365 days = $131 /year.
So the pump which was $50 cheaper, actually cost you $131 per year more to run. Certainly no savings there
Also - check this site - very good info on water pumps
Please don't be too quick to settle on Mag Drive - especially for a bedroom application and especially if you need better then 500gph.
Hope this helped as well.