Hi Mike
Have you ran a sweep with something like CCleaner on the Registry Cleaner?
and no Joy?

Then I suggest opening Regedit via the Run box on the Start Menu
Click Edit and enter in the search box "sonic backup" and delete any entries Take your time just to delete the Line in the Open folder or the open Folder if its named the same thing? Press the F3 key to go to the next find (there will be several entries)
TOP TIP Do a "search" without deleting anything first,to get used to the Layout OK?

PS I had a "Paltalk" Item showing in My start up Folder the other day even though the program was removed a few weeks ago. Neither CCleaner nor Easy Cleaner showed it!

And impossible to remove too....Had to resort to Going into the Registry(Via Regedit) and Manually delete the links from there(There is a Corresponding Start-up folder in the Registry too @ HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\MSConfig\startupreg) Had 5 links to go in total

Did run CCleaner again and No Items were found to go