Rear wiper has mind of its own

[sptravis]

The rear wiper on my 2003 X5 3.0i seems to have a mind of its own. It goes on its own, even when the rear wiper switch is off, but at an unpredictable and infrequent rate. It may go once or twice every ten minutes or so that I am driving. The rear wiper works fine when the wiper switch is on.

Any ideas what the issue may be?

Thanks.