Why does Caroline Bingley disapprove of Wickham?

She disapproves of Wickham because she believes he spreads untrue rumors about Darcy, whom she hopes to marry.

"Let me recommend you, however, as a friend, not to give implicit confidence to all his assertions: for as to Mr. Darcy's using him ill, it is perfectly false; for, on the contrary, he has been always remarkably kind to him, though George Wickham has treated Mr. Darcy in a most infamous manner. I do not know the particulars, but I know very well that Mr. Darcy is not in the least to blame, that he cannot bear to hear George Wickham mentioned, and that though my brother thought he could not well avoid including him in his invitation to the officers, he was excessively glad to find that he had taken himself out of the way. His coming into the country at all is a most insolent thing, indeed, and I wonder how he could presume to do it. I pity you, Miss Eliza, for this discovery of your favourite's guilt; but really considering his descent, one could not expect much better."

Source(s): Pride and Prejudice/ Chapter 18