After about an hour of highway speed driving there is an erratic clunking underneath the car towards the rear. Initially I thought it was the exhaust clanking around, but I removed the exhaust and it's still happening.

I've read that this is often the rear CV axles. Mine look good, boots are solid. Could still be the issue but wanted some feedback here. It sounds like someone whacking the underside of the car with a mallet. Only when fuel is applied, not when coasting. It's also not exactly rhythmic, random in intensity.

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1984 300CD