You could get around this by using a fade in Audacity before the noise becomes audible. You can probably see the noise in Audacity.
And there is some background hissing (you can hear it at the end, while the final chord is fading out), but I wouldn't worry about it, it's pretty normal. You could easily equalize it out, if you wanted.
I see, I'm still wondering whether it would be there while using the usual sound and not grand piano, it would be difficult to simulate now, since I have no idea what the sound setting was (the level on the piano and booster in alsamixer).
btw this is audacity pic
30 + 35sec
So when it comes down to the settings, I'll stick with 44.1 and 16bit, compression MP3 to the best or second to best, or FLAC 16bit, 8