I try to engage mine before I need them. it is like the transfer case starts spinning stuff before the IWE gets engaged. But you should keep a good eye on the lines. I test my system on tire rotation. just make it part of the rotation. once I get the truck jacked up I pull a vacuum. take the tire off the front and then the back roll the back to the front and then check the vacuum.put the tire on. I pull the vacuum on the entire system.I've been having a similar problem. If i engage 4x4 on a hill I'll get a pretty loud bang after a few feet. Sounds like its slamming into gear or something. Only does it if i engage 4x4 on a hill. if i engage on flat road and drive a little ways, i don't have any issues when getting to the steep parts. I should just suck it up and replace my IWE lines as well. Seems like an easy fix or at the least, good preventative maintenance.