I stopped listening for it a couple weeks after I replaced the bags, once I was convinced they were holding up.

But I have noticed it kick on a couple times, only when we're loading/have loaded up the trunk with stuff when we're taking off for the weekend. Haven't heard it just day to day driving, but I wouldn't expect to, that means it's leaking. If the rear end isn't sagging, I don't think you have anything to worry about.