Rolling and clicking?

[Robert W Obrien <rwo@u.arizona.edu>]

Thanks everyone for the fine advice so far. Aside from the usual suspects,
the 5kcst is just screaming along- but what is this confounded *noise!*

Situation:
Any gear, any speed over 40 mph. Even w/engine off.
Sounds like tappets,  to give an idea of the noise.
Click click click click click.
Completely stops under 40.
Either goes away or is drowned out over 75.
Replaced or inspected:
CV joints new (changed noise not a whit)
Wheel bearings good. 
Brakes within spec
No pebbles in tire treads:)

So, what now? Anyone had this happen? 

TIA, Rob
1987 5000CS Turbo. 161K. Runs like a Rolex. Ticks likewise.