Excel ghosting information

This has been driving me batty for some time.  Sporadically, I'll type something in one cell and it will appear over another - not wiping out the info in the cell it's over, but blocking me from seeing it.  This  happens with text, numbers, even fill colours.  And it even sometimes will appear on a different sheet in a workbook.  Anyone else come across this issue, and how to fix it?  It's not like there's a cell linkage, for it doesn't happen all the time, and the chosen cell to obscure seems to be random when it does happen.