Was at a dealer for other reasons and had them check the noise today. It took some time for them to even notice it. They think it is the traction motor, but they said it is hard to pinpoint the source exactly so could be the reduction gear too, basically the noise was coming from the motor area when they lifted the car, so not a CV joint which is consistent with the symptoms as turning the wheels doesn't make the noise louder. Given a new traction motor is a $9.5k job the recommendation was to just drive the car until things get worse, which I'm going to follow to the letter.
'11 SL, totaled
-1CB@33k/21mo, -2CB@53k/33mo, -3CB@68k/41mo, -4CB(41.5AHr)@79k/49mo, -5CB(38.85AHr)@87.5k/54mo
51.1AHr, SOH 80%, 150k miles9kW Solar