Quiet is very important to me. I am also often listening to music louder than the noise--lol, ~35db noise + ~85db+ of music. (I have a sound level meter...they're pretty neat)
But you lose some "quality" ... by hearing the background noise, you are probably more than cancelling out any benefit flac provides. I am nowhere near silent computing but I try to make each PC a little quieter. That means less heat, noise, power consumption, and newer components. I would like a 100% silent PC...and I could almost have it. The hard drive isn't a big culprit. Besides, most my data comes over the network from the server. I wonder if I could get one of those new solid state HDDs from Sandisk? If they aren't outrageous--under $200--I might consider it. Of course then I'll be spending more to get passive cooling on everything. What about the CPU?
Or just buy a readymade, silent PC.