that happened to me before
whenever I put the car on P or N when the car is not moving (with engine still running) and no noise, but as soon as the gear on D (load on the car) the was this noise and came from belt tensioner..
Dealer replaced the tensioner under warranty.
This belt tensioner shouldn;t have anything to do with your harmonic balance.
You just have to replace it when they go bad..
don't delay replacing it, since you don't know how long they could stay on broken/worn like that..
if anything that I could not stand on my car ......
no no it's not dirt, its noises like that....
God noises like that could get under my skin, ...
and to notice noises like that very soon in the stage is always a good thing
Regardz,