There are times when it "sings" if the stepper motors are moving exactly the same direction and speed.  Most of the time you'll just hear the motors going about their business.  My kids thought some of the sounds were pretty funny to listen to.

It's not "loud" by any stretch of the imagination, but could be annoying if someone is sitting in the same room trying to do a quiet activity like reading a book.

Hello all, first time poster and hopefully soon to be owner of a Solidoodle.

I've been wanting to buy a 3d printer for quite some time now, but the amount of choices out there is staggering.
Eventually I saw the Solidoodle, and it seems that it fit's most of the things I want in a 3d printer. Price & Size mainly.
The problem is that I live in a small apartment and have a toddler running around.
So I was thinking of the enclosed Solidoodle expert ( build ). But how much sound does this thing really make ? Can you sit in the same room and "not notice it" ? Since it's going to run for hours while i'm at work, I don't want my wife to go crazy and trow it out
And the second question is, how will it run stock on PLA, without modifications ?
I don't want to use ABS because of the toxic fumes, and the toddler running around. ( how toxic is PLA anyway, will the entire place smell of this thing ? )

I don't know about a sound proof enclosure, or an enclosure of any kind, but the open frame printer is not really quiet. 

Not loud, but you will certainly notice it in a small room.  I can leave it running at overnight and I can't really hear it in the other room, but when it's sitting only 5-6 feet away, and you're trying to listen to your TV which is only about 8-10 feet away on low volume, I have to put up the volume sometimes during softly spoken passage.

Edit:
I just did a little test using my phone and a sound Meter App.  The phone was set in a cradle, approximately half way between me and the printer (about 3 feet in either direction).

The room ambient noise level measured between 32-35db. When printing, noise varies depending on the printer movements.  For large, smooth moves, it measures between 53-56db.  Short jerky moves like small perimeters and small zig-zag infill can get the level up to about 59-60db.

Adding the TV to mix did not  seem to increase the noise level over the noise of the printer, it was still between 53-55db.  My wife walked into the room and while we were talking in a normal tone of voice the meter registered about 64-66db.

I've been wanting to buy a 3d printer for quite some time now, but the amount of choices out there is staggering.
Eventually I saw the Solidoodle, and it seems that it fit's most of the things I want in a 3d printer. Price & Size mainly.
The problem is that I live in a small apartment and have a toddler running around.
So I was thinking of the enclosed Solidoodle expert ( build ). But how much sound does this thing really make ? Can you sit in the same room and "not notice it" ? Since it's going to run for hours while i'm at work, I don't want my wife to go crazy and trow it out
And the second question is, how will it run stock on PLA, without modifications ?
I don't want to use ABS because of the toxic fumes, and the toddler running around. ( how toxic is PLA anyway, will the entire place smell of this thing ? )