When I open my regular xls file, Excel asks me
This workbook contains macros. Do you want to disable macros before opening the file?
However, if I open Visual Basic Editor (alt+F11) there are no Modules listed and I am not aware of any macros used, the most complicated things are some matrix formulas.
Edit: The problem only occurs if I save in xls. If I change as xlsx (which sadly is not a solution for me) Excel does not ask.
Edit 2: The problem occurs as soon as I try to copy a sheet to another file and save. Even if I remove that sheet later, excel keeps asking me about enabling macros. Here is a test file for reproduction.