Excel Keeps Recalculating When Opening New Spreadsheet

Some of the reports I run for work are very complex and involve me having to export system data, open it as a CSV file, and copy/paste into my reporting workbook. As our business is seasonal and our reporting dependent on many formulas, pulling the data together can take awhile. If I disable automatic calculations in favor of manual, my work does go faster (and I simply calculate the workbook sporadically). However, Excel will still calculate for 3-5 minutes each time I open a new exported worksheet to copy/paste from. So a report that should take 20 minutes can take up to an hour. How do I stop Excel from calculating new worksheets upon open? There are no formulas in the CSV files and calculation is already set to manual. I am using Excel 2010 Prof 64-bit. Please help if able and thanks.