I never noticed this issue because I never use my phone on ringing... it's always on vibrate, so it doesn't produce sounds.
If you don't need your phone to ring during the night, you could put it on vibrate to workaround this problem.
Anyway, I agree that it should be fixed asap.
OK, I think I know the events which cause the 820 to randomly wake up and "ding" after the GDR2 update.
When I initially set the 820 on the charging stand it "dings" and charges to 100%. Then the charger goes in Standby mode where it checks the phone occasionally to see if it needs a charge (the charging base light comes on for 10-20 secs). If the phone is still at 100%, or close to it, the charging base returns to Standby mode. After some time the phone charge drops a couple percent and the charging base detects it needs to add a charge and the charging base light comes on and stays on. The phone enters charging mode.
Here is what's different from before. Previously, when the phone entered charging mode from the base, after already being fully charged before, the phone didn't wake up and "ding" again. Now the phone wakes up and "dings" every time the charging base puts the phone is charging mode. This can happen 2 or 3 times overnight. VERY ANNOYING!!
I don't know if this happens with the charging cable since I only use wireless chargers. Where can we let Nokia/Microsoft know about this new bug????