Since my electrical repair was easier than expected, I've got some extra gumption available and may as well address an old, more nebulous issue.

I occasionally hear an odd, heavy, dull thunking noise coming from the rear of my '86 240 wagon. It not a rhythmic, repeating sort of noise, just a single thunk, as if someone had hit some very solid part of the frame with a small sledge. It usually happens when cruising steadily at higher speeds, though not when accelerating. It seems to happen when the car is just easing along the road, no severe load on the engine or suspension. When it happens while cruising it can happen several times within a few minutes, then go away. It also happens when decelerating from higher speeds, such as near the end of freeway ramps when I've almost come to a complete stop. These are not hard braking situations either; it's just as if the car is relaxing a bit and... thunk!

It's been doing this, on and off, for a couple of years, but the car doesn't get driven a whole lot so it's been a low priority.

If I had to guess I'd say a suspension bushing might be shot and/or simply gone, and the thunking might happen as the loads on different parts shift. I haven't done any suspension work, though, so I'm not sure of the likely places to look. Ring any bells?