Front end noise caused by 2" coil spring retention?

[earl84]

My 66 C20 is finally on the road, just in time for a move to Colorado, where it will become my daily driver. Well, actually it'[s been off and on the road several times for various projects, but it is finally (almost) complete. I got all the things done that REALLY need to be done to make it driveable, there's a million other little things to do.
My question is this. When I drive it, there is a sort of clunking noise when I go over bumps at a decent speed, like anything over 15 mph. It does not happen all the time. I have replaced the entire front end with a 79 crossmember, and replaced every single wear part with new Moog components. Yesterday, I took the wheels off, jacked it up, felt around, nothing obviously loose. I retorqued everything, all good. Nothing is loose, nothing. No endplay in the wheel bearings, calipers are solid. Checked the driveshaft for mounting. It is newly shortened and balanced with new Ujoints, new center carrier bearing.
The only thing I can think of is the lower end of the 2" lowered coil spring moving around slightly, but I don't see any evidence of that, such as metal flakes, paint scarred up, nothing. I am at a loss, and it feels completely, 100% solid, no wandering, no weird braking action, no steady noise, nothing. I did every conceivable type of driving to help ID a problem part, and the front end is very very solid.
Is there a retainer for the lower coil spring? Anyone have any other ideas? Unfortunately, I will not actually be able to do anything with this for a while, since this afternoon and tomorrow are devoted to packing a Uhaul and loading the truck onto a car hauler. May have to take it to a mechanic in Denver and let them check it out.

BTW, sorry for the dissertation, just wanted to answer the questions that were sure to come up. As always, thanks for replies, and I LOVE this board.