i have an 08 standard TL and i started noticing a whirring noise when its below 40F degrees especially when its wet outside so definitely related to temperature and humidity. its most noticeable when idling and subsides above 2000 rpm.

it started maybe last winter '11-'12 when I was I lived in North Texas (drier climate but if it was rainy it would be more prominent). and use to stop after the car warmed up a bit after a few minutes

Now that I live in DC (more humid) it happens in the 40s even if its not wet (but I'm assuming the air is still more humid vs when its not rainy in TX) and it does not stop after driving for a while and the car is fully warmed up like it use to in TX

because I now live in a different environment, i can't tell if it has gotten worse over time or if it is because the air is more humid in DC.

any idea what this could be from? It's a high mileage car as I put in about 350mi/wk and am now at 77k miles.

never had the issue in warmer weather even if it was raining outside so i can conclude cold temperature is the driving factor with humidity exacerbating the problem.

still happens if i turn the fan (a/c & heater off) so its definitely engine related

any idea what this could be?

 

check out the serpentine belt tensioner.

You can remove the belt and start the car momentarily to see if the noise is gone.

 

Please check out service bulletin tsb 08-031...

 

This TSB states specifically that the noise occurs after the engine is warmed up. His problem is when its cold/humid and goes away when warmed up. I dont think this TSB applies. Im having the same problem as well. After 5 mins it goes away when engine is warm