Obviously not a problem with this phone, but with my old Bionic it usually died about an hour before bedtime so it would reboot when I plugged it in and it was LOUD. I was always worried about waking people up in my house, but that phone was easy to keep quiet if you kept your finger over the speaker. Even so, the noise was just obnoxious.
Honestly, I'm not even sure what this one sounds like, I think it's only rebooted once at the store and once when it got new software, but I don't recall it being anywhere near as annoying.