Everytime I turn my windshield wipers on, they violently strike the base when they decend back down, and it's VERY loud when they hit it. It only happens when the car is at a stand still, when i drive they don't hit the base hard. What could be the problem and what would be the solution ?

 

you can remove the nut that holds the wipers on. it is a spline and you should be able to move them a notch or two up so that they dont hit any more.

 

that may keep them from hitting... but more than likely poor adjustment isn't the root cause.

OP: my guess- you're wiper linkages are shot. the joints are made out of plastic... so they break/wear out.

when they are in the rest position move one back and forth slightly by hand. if you can feel them knock, or they move more than an inch or so without much effort time to replace the joints. it's not hard either-

1. remove the wiper arms
2. remove the black plastic trim/cover at the base of the windshield.
3. unplug the wire harness running to the motor and undo the handful of bolts holding it in.
4. set it on the bench and pop the old linkages loose one at a time, paying close attention to the length of each one and it's replacement.
5. install reverse of removal.