Greetings, I have a system comprised of 8 zones and 8 SRS (I believe these are Hunters professional heads) 360 degree adjustable spray heads each. I notice that when a zone goes off a few of my heads will slightly twist a few degrees as they are recessing back into the head shaft. This means the next time they pop up they are off by 10-15 degrees. Any thoughts on why this is happening? Not all of them do it, some stay aligned forever. Some that are straying from my desired ARC have been replaced...