Check out the Fantech bath ventilation systems. Only a small vent opening needed in the ceiling, with the blower remotely mounted in the attic. I have these in all of my bathrooms. Very effective, very reliable and absolutely silent. So silent, in fact, that you probably want to also get the timer switch so that the fan will turn off after the number of minutes you select. Without the timer, you'll forget to turn off the fan because you won't hear it running. Click on the link below for more info.

Here is a link that might be useful: Fantech Bathroom Ventilation

This looks great. I'm a little annoyed at myself because I went with the Panasonic Whisper Warm, which is supposed to be incredibly effective and silent. But on the downside, mine is really huge, and now that I see the opening in the ceiling for it, I'm pretty disappointed that I didn't shop around for something smaller. I think it is really going to detract from the beautiful ceiling light I purchased. (Our project should be done in about 3 weeks, so it isn't all installed yet. Our bathroom isn't enormous, so the vent is probably only 5 feet or less away from the central light). Anyway, I'm hopeful that I'll be able to ignore looking at it, but if I knew there was another silent/effective option that was smaller, I would have definitely jumped at it. So good luck with your research, I hope you find the right combination of features you are looking for!

As far as I recall the Fantech does not have a heater. You can always put your whisperwarm on ebay or Craigslist and get the Fantech if you don't need the heat feature.

Good luck!