General :: Cp Adds Exclamation Points When Copying Very Large Text Files?

For my research I have some very large files that are basically millions of lines of ten columns of numbers. These files can be up to 5 GB in size. Recently I noticed that when I made a copy of one of my files, some exclamation points appeared in it where there should not be any: in front of random numbers throughout the file. Making another copy of the file would result in exclamation points in front of different numbers in different parts of the file. Doing this many times has given me up to four exclamation points in different parts of the file. Sometimes the file copies just fine without producing any extraneous exclamation points.Additionally, I have occasionally seen a "^K" where there should be a newline (the data that should have been on the next line was instead on the previous line with a ^K in front of it) in copies that I have made of my files. I don't know if this is related or not.