300 f/4 AF grinding

[sandyquandt]

Hi!

Noticed today that the autofocus, which I rarely use, is beginning to sound 
like a weed-whacker...well, maybe not *that* bad, but it's making a high 
pitched squealing sound when the AF operates. It focuses fine manually and the 
AF works; it's just very noisy. Of course, the warranty has expired... :-( 
Anyone have an idea of the cause of the problem and/or the cost of repair?

Thanks!
Sandy