Clunking could be the rear U-Joint. I just had my driveshaft replaced for the same symptom.
I tried the Guibo and the Center Bearing first (because combined they are less than $100) but finally ended up spending the $500 for a new driveshaft (original had about 150,000 miles). When the mechanic got the driveshaft out, he said the U-Joint was so bad he was surprised it even stayed together
Very smooth with NO clunking now.