Ceiling Exhaust Fan -How loud is .5 sones?

Mumbles,
Excellent numbers, greatly appreciated. After carefully consider all possibilities, I've decided to go back to my first plan.
2chnlben,
Great to see you, Shadome, and some others have the technical ability and taking this hobby seriously.

Could it be as quite as the little computer exhaust fan, any1 ?
Thanks

"I belive Home Depot has a display where you can hear various fans."

Thanks Jd,
It's great if they have many of them side-by-side for testing and I'd be greatly delightful & will keep that in mind.
However, unlike my WELL TREATED HT room, the noise inside home depot is tramendously loud. It's like audition new pair of speakers sharing a room with a jet engine running. Lol.

"Short answer, (In my opinion), If the fan is near you and you have a very quiet room you will hear it."

Thanks Albert,
If any1 can confirm .3 or .5 sones is as noisy as the back of the computer fan, that'd be ecellent and I can live with that.

Thanks Aby,
Since I wanted to avoid ANY unwanted sound in my HT room, the design that you mentioned (relocate the fan futher away) was first on my drawing board. But if .5 sones is an exeptional number, then I can live with it. Problem is, what is .5 sones equivalent to realife example?
This is what you are talking: http://www.youtube.com/watch?v=B-qWg60xFtY

BJ,
Yes,the exhaust fan must run when the system is on to get the heat up on attic. Reason I'm looking for maximum quiteness is because I listen to soft music on low volume normally at 2 to 4am. So basically, at these hours, I will hear everything else as well.
I just read an DIY article about an exhaust fan with .5 sones and the author gave a real life example: In his bedroom, the fan ran very quite that he was 10' away and he couldn't tell if it was On or not. That's a very good info for me.