I think there are two possible causes,
1. If this is the same tone you get when first connecting the charger, the charger may be disconnecting then reconnecting (at least logically if not physically), so it would be worth testing with a different USB power adapter and magnetic cable, according to what you have available. I know you have the adapter which charges your iPhone, so that would be perfect for testing.
2. Something actually wrong in the watch, either software or hardware. Software is a prime suspect because it started with the update. You could try unpairing and re-pair to your phone again to force reinstalling the Watch software. If that still doesn't work the last resort is Contact Apple Support and arrange to get it checked by Apple. Don't just skip to calling Apple Support, make sure you already tried the earlier steps because they will want to try these first.
Don't forget you can charge your watch at any time, you don't need to wait until overnight for testing the fixes!
Just thought I would add to the many on here, my watch a series 4 has started doing the same thing, in the last month or so.
This started happening to my Apple Watch (series 4) about a month ago. I can no longer charge it on my nightstand or it'll wake me up throughout the night. This really needs Apple's attention!
Exactly the same problem for me when I updated the OS to 5.1.2 It’s fine until it gets to 100% then it keeps chiming every minute or two tried all the fixes apart from unpairing and installing as new, apple need to release a fix for this problem.
I've been having this problem for quite a while (series 3 42mm Nike). I knew it wasn't the charger itself because my series 4 charges on the same charger without any problems.
Eventually I tried charging my s3 on my wife's charger (charger is from a series 4 watch, but should be the same) and the issue doesn't present itself. Doesn't make any sense.
Apple has had my watch in their possession at their repair center but couldn't duplicate the problem so sent it back.
This is extremely frustrating.
Apple finally today told me it's a software problem and to bear with them. I just don't get how something in the software could present an issue like this. Mainly the fact that it works fine on my wife's identical charger, but not on mine that came with the watch.
Oh that's strange. Apple Support finally came back with a response from their engineering team. Apparently All Series 3 Aluminium's made after September 2018 exhibit this issue as it's an incompatibility between the old plastic chargers and the new ones. And the only fix is a stainless steel charger or an Apple Watch Dock.
I bought my watch in early 2018, so this answer they gave you cannot be accurate.
My series 3 watch started chiming at night after the latest 5.2 update. Happened every 10 minutes or so from about 4am (so fully charged). Last week I bought a new apple charging cable in case my original (apple supplied with watch) cable was the problem. Strangely everything seemed sorted and no night time chiming for for 6 nights but last night the watch started chiming again in exactly the same way as before. Driving me mad and I then lie awake until morning!
I broke the screen on my aluminium series 3 and have had to buy a new one as not covered by Apple. The new one is doing this as well but the old one didn't. Thought there must be a setting on the phone but no!!
I'm having this exact same problem. It literally started out of the blue 2 nights ago. Apple Watch 3 series, OS 5.2.1 purchased July 2018.
Frustrated. I read this whole thread, and decided that maybe the magnetic connectors were dirty. I wear my watch everyday, and obviously to work out... i'm sure they're dirty and thinking maybe this is the problem. I do not normally wear mine in the shower as I'm paranoid it will get ruined. I also did a hard reset, and unplugged and replugged the charger. Will see if any of those things make a difference.
It is likely this is a hardware problem in individual users’ equipment, because it does not impact every watch, or even every watch on specific software. What we know is that it seems to happen when the watch is fully charged, and the chime occurs when a watch detects charger power has just been applied. What we don’t know is whether this is a hallucination in the watch charging circuit, or a genuine break and resume of power to the magnetic head which would implicate the power adapter and charging cable, or maybe even connection to the AC supply.
Whatever, the fix MUST come from Apple, and you can only achieve that by getting your watch and charger tested as a pair at a Genius Bar appointment. Ideally, go in with the watch as near full charge as possible so you don’t have to wait so long.
You really shouldn't need specifically a stainless steel charger. When I had this issue, I tried my wife's charger that came with her watch, and it made the issue "go away".
It's kind of sad Apple still doesn't know how to fix this.
My Apple Watch 4 would also chime on the charger. I tried a lot of things no help. I found out tthat the watch had to be on the charger perfectly centered and at full rest. The charger must mate perfectly with the base of the watch. BAM no more chime. Even my wife noticed that it was gone.
The Apple advisor i spoke with said the chime was to get the watch off the charger as well as indicate it was fully charged. Not good to leave it on the charger past full.
I have a a stainless steel watch and bought a cheap charger that feels plastic. That must be it!
Mine is doing the same chimes every 10 secs or so when on charge. Only started after os6 upgrade.
Continuous chime when charging
