Clunking sound on highway...

[burntcloth]

While driving my 82 300TD on the highway today, a rythmic clunking sound began from the middle or back of the car (hard to tell). When I slowed down, it became more noticable, but stopped around 10mph. Upon start-up, the clunking was gone, but resumed 15 minutes later.

My rear CV joint boot is leaking oil. Would a CV joint low on grease cause a noise like that?