It's just the turbulent sound of nervous shorts exiting their positions, now that the short interest numbers for September are in. Up about 3% from August and sitting above 2.8M shares (still over 8% of float). With earnings date coming soon and these numbers, I wouldn't want to be on the short end of the stick.
First, stop watching the day-to-day on this stock: Some of you folks get way too excited about the moves up on down market days and too worried about the moves down on up market days. Keep this in your portfolio for the next five years and I strongly doubt you'll be disappointed.
Second, let's hope this company avoids the worst possible fate of being bought out by GE, MDT, or whomever. It's doing fine just as it is, and any merger will, IMHO, kill the goose that is laying the golden eggs.