2006 Subaru Foreter 2.5X vibration

I recently bought a 2006 Subaru Forester 2.5X (approximately 600 miles).

Noticed in the last couple of days that when the car is in park with the engine idling that there are intervals (approximately every 3 to 5 seconds) when there is a slight rumbling vibration.

This seems odd for an new car has anyone had a similiar experience?

Thanks
sol