Another thing you could do is get under the car and inspect the rubber items associated with the drive line. You'll want something to pry on them with a bit. Visually they might appear good but when you flex the rubber you can see cracks and what not.

Mine made a thumping sound under load when going up a hill or sometimes under harder acceleration. I looked and everything seemed visually ok, but leveraged the trans mount with a prybar and could see bad cracks.