Try replacing your swaybar bushings. I'm guessing they're worn out after 3yrs and have enough play to let the swaybar bang against the subframe while under load. They're pretty cheap at $6.50/ea from BAT.
You might also consider replacing the swaybar bushing brackets if your originals are deformed enough. They'll cost you at least $60 for a new pair.
How do the circle retainer clips that BAT welds on its swaybar look? Are they bent, deformed, or missing? They could be a possible source for the klunk.
