IMAC Notification DINGING constantly even with settings OFF

Bitdefender at the least is contributing to the problem!!!! Any third party AV app is completely unnecessary and is potentially damaging to Mac OS, Bitdefender is among the worst.

Mac OS does not require nor does it benefit by adding ANY third party AV apps. They have the exact opposite effects that users want, they Mac OS slow, appear buggy and make Mac OS do strange things like you are experiencing..

please locate the developers uninstall instructions and fully uninstall Bitdefender.

See if you have any websites listed in Safari's Websites settings pane. If there are any delete all and set the "When visiting other websites" to Off:

Don't know if it will stop the dinging but worth a try.

BTW, do you have any of the following third party apps installed on your Mac?

·      Antivirus Apps

·      Cleaning Apps

·      Security Apps

·      VPN Apps

·      Maintenance Apps

There is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This documents describe what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community and Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is designed solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

All Bitdefender does is reduce your bank account by $80-$90 per year.