Ideas, please.

I have in inground sprinkler system, that comes off of the water supply to the house ahead of my Culligan 2 tank (Mark 100?) softener. ONLY when I use the sprinkler, NOT with other water use, I am getting a severe vibration in the water line, which seems to be coming from the softener. IT GOES AWAY WHEN I BYPASS THE SOFTENER!

Not sure whether to call Culligan, a plumber, or what the problem might be. Your help and ideas are appreciated!