transmission cooler lines tapping-too close to O2 sensor?

[Sunliner]

Yesterday, my Blazer starts making this "clacking" noise after it gets good and warm.
I goof around with it for a while, and come to the conclusion that one of the lines from the radiator to the transmission is contacting one of the O2 sensors coming off the manifold. The line is just a few millimeters away from the sensor and apparently when things heat up and expand, they touch.

My question is, does anybody know how close these lines are supposed to be to the sensor and manifold?
I never paid any attention to that part of the truck before..no reason to. I'm wondering if a mount or something has slipped and brought these parts too close together.

-Mike