Mine is worse with the AC running as well, and the dealer tested all pulleys, alternator, ac condensor etc. It's worse because of the extra load on the engine at such a low RPM.
The reality is this, it idles stupid low, (600ish rpm when warm?) plus our torque converters are very tight to help with fuel economy. It's my opinion those two things cause it. For them to not shake apart I'm guessing they have a pretty big counterbalance on the crank. I asked the dealer if they could raise the idle a little via computer to see if it helps, but they claim they can't.
sometimes tough to diagnose,
when i was getting a rattle, sounded like valves or timing chain,
dealer had a hard time pinning it down,
all pulleys checked out fine,
rattle only occurred under load,
dealer took each pulley out, with process of elimination swapping each with a known good pulley in the shop, they narrowed it down to the alternator,
even when removed pulley seemed fine, couldnt tell it was the cause,
but under load it was failing,
took quite some work to diagnose but they did it,
also while he was in there they replaced my water pump under warranty,
did so , so they could put the extra labor hours under warranty work, and i only paid for 1 hr labor and part cost for alternator
