Cannot find solution to this problem on threads so here goes: 2006 Legacy sedan with auto transmission and 130K miles. In slow stop and go traffic I can feel and hear a metallic "clunk" upon light acceleration, and sometimes another one right after it on deceleration. Checked all joints, tranny mounts, misfiring, drive train--could not see anything but may have missed something. Thought it was the tranny mount but the two rubber blocks look and feel solid. No problem under hard acceleration/deceleration. Feels like something heavy is loose, and is shifting its weight in the opposite direction that the car is accelerating in. Thanks for ideas and best guesses, and ideally how to diagnose too if possible!