I have a kitchen aid stand mixer and the head

This sounds like an issue of beater to bowl adjustment, which can come out of alignment naturally over time and with use of the machine.

If the flat beater is striking the bottom of your bowl, this may cause the locking mechanism to loosen and may cause the mixing head to "bounce" during use.

Your Use and Care Guide will cover the "beater to bowl adjustment," which you can do at home in a few minutes with a flathead screwdriver.