Apple Watch making sound in sleep mode

If all settings normal but behaviour is irrational there is a progressive hierarchy of  remedies.

Hopefully you will not need to go to the end of the list!

First make sure you are not using VPN or VPN adblockers or security apps on the iPhone. They can wreak havoc and protect nothing.

Start by force restarting the Watch and paired iPhone at the same time:-

Force restart the Watch

i.e. p ess and hold both the side button and Digital Crown for at least 10 seconds, then release both buttons when you see the Apple logo. Then while Watch is restarting,

Force Restart the paired iphone   Force restart iPhone – Apple Support (UK) 

You may also want to make sure the software on the watch and iphone  are both up to date to the same level. Updates are in pairs. eg iOS16.4 and watchOS 9.4 go together

Update your iPhone or iPad - Apple Support and

Update your Apple Watch - Apple Support 

Test it for a while. If it is still misbehaving...

Unpair and set up again

 Unpair and erase your Apple Watch – Apple Support (UK) 

and then set up again - takes about 20 minutes

Set up your Apple Watch – Apple Support (UK) 

If necessary unpair and setup without restoring the backup

If you've completed that troubleshooting and the issue is still not resolved, Contact Support. 

 Click here > Contact - Official Apple Support

or phone numbers  

Click here > Contact Apple for support and service - Apple Support

and or Genius Bar Reservation and Apple Support Options - Apple

Firstly third party charging stands have been known to do this. Try the original puck.

Secondly schedule a Do Not Disturb ficus for night time on your iphone and ensure your Watch mirrors focuses.

Define what you mean by Sleep Mode please. What have you set?

Did you try Do not Disturb?

What is tater sound?

Did you manage to resolve this? Mine is randomly now doing the same. Messages coming through with a loud ping while on sleep focus.