I have some slop in the receiver/head also. Part of it is the brand of receiver and head you use, some have closer tolerances. Part of it is wear, also. If you have lots of time to mess with it, you can make a nylon/teflon pad for the head to ride on, it should hold up pretty well.
The head moves in the receiver on ours as well, but the only time I hear a "clunk" is when I walk into it
...ouch.