Wipers

the wiper arm goes on a "stud" with grooves in it , they may be stripped for what ever reason , see what kind of play is in the arm when they're off . and let us know how problem is resolved .

I have the same problem with my '03 and it is the wiper arm slipping on the splined stud as has been mentioned above. While you could start replacing expensive parts, I've had good success simply tightening the nut that holds the wiper arm to the shaft. You can crank it down really tight without breaking it. Make sure your wrench is the right size so you don't round off the nut or you'll be in trouble. You will need to have the hood up and may want to park the wipers in the up position to do the final tightening although you'll need to start with them down so you get the arm positioned correctly on the shaft. Even after tightening mine I've had it come loose again later so I actually carry a wrench with me in the car in case it lets me down while on the road. In my climate a failed wiper during a heavy wet snow storm can leave a person stranded.