The global system notes differ from other system notes because while other system notes give information about changes that affect your customers (customer changes, loan changes, lease changes), global system notes show changes that affect your company configuration.
The global system notes can be viewed by navigating to Settings > Company > Global System Notes inside your company account.
Click Show Filtering Options to expand the filtering options. You can filter the global system notes by note category, agent user, or date. This should help you track down who made changes in your company account.