WinPatrol will do this for you. The free version is sufficient, I ran it for years and it did just what you are describing, among other things...
It runs in the background and a dialog box pops up with several options whenever something wants to modify the startup entries..
I am not affiliated with this product in any way, shape, or form.
Another option for analyzing your start up (not so strong in the notifications area but is a powerful tool, nonetheless):
AutoRuns
This utility, which has the most comprehensive knowledge of auto-starting locations of any startup monitor, shows you what programs are configured to run during system bootup or login, and shows you the entries in the order Windows processes them. These programs include ones in your startup folder, Run, RunOnce, and other Registry keys. You can configure Autoruns to show other locations, including Explorer shell extensions, toolbars, browser helper objects, Winlogon notifications, auto-start services, and much more. Autoruns goes way beyond the MSConfig utility bundled with Windows Me and XP.
I am still using StartupMonitor in Windows 10. However, it does only monitor autostart entries of 32 bit applications. But this works for me reliable since Windows 2000 (or Windows 98?). The autostart monitor utility detected some unwanted applications in all those years. – Thorsten Albrecht – 2017-07-28T17:20:55.843