The wiper blades are smacking into one another and overextending their normal path. Could it be a wiper blade motor or switch problem?
It sounds like your may have some wiper blade linkage problems. I would have a technician come out and remove the wiper access panel and inspect the linkage connected to the wiper blades. They might just need to be removed and readjusted. I would recommend having your wiper system inspected to have the proper repairs made.
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