I have a 2013 RDX with 21k miles on it. The car is driven occasionally. I recently noticed a weird whirring sound from the car, Its noticeable when i take my feet off the gas. It feels like something is working against the engine. The car drove pretty smooth earlier and suddenly this sound and drag has appeared from no where. Has anyone have/had the same problem? Any suggestion what might be wrong. I recently did the 3rd servicing on the car (A16, if I am not wrong).

 

What You are experiencing is normal for the RDX.I noticed it right away when I bought mine.Apparently, Acura has a noticeable downshift coming to a stop,or driving slower.
I drove a friends 2015 RDX with 8000 miles on it.It reacted the same way.I also drove a 2017 loaner, when My airbag inflator was replaced.It drove the same.It feels funny,but, when You are getting 26 mpg You won't care how it feels.The other feeling that is weird is the noise at about 39 mph.I think it is the engine running on fewer cylinders.You will get used to it and love Your RDX!

 

Property remanufactured transmission should be as good as new. The only downside is the increased human factor that examines broken/worn parts and puts things back together.