I have a whirring/growling noise that starts when I shift in to drive and only when I am on the throttle/accelerating. If I let off the fuel pedal/throttle, the sound immediately stops. It is a reciprocating/whirring noise. Most noticeable when it is cold and as the engine warms up, it dissipates. It is higher pitched fluttering almost. I would not describe it as grinding. Shifting is good. Sound is consistent as well with shifting, i.e. it will stop during shift and then return. Seems to be coming from passenger side of engine bay. Tough to diagnose since the vehicle needs to be in motion to hear it. 2012 XC90 FWD. Where do I start?

 

I'd start by inspecting the axles - any torn CV joint boots, signs of oil leakage etc? As to the tranny, how many miles - have you ever had the fluid checked ie drain fill? If you do that, you can run through filter paper to check for any bits.