For the last couple of months my car ('11 3.6R) has had an intermittent buzz and vibration from the rear passenger side when stopped at a red light or parked with the engine running. I put the car on ramps at home and traced the vibration to the gas tank.
I pulled off the plastic shields around the tank and placed my hands on it. Sure enough, when the buzz started I could feel the vibration. I figured it must be the pump. What else would be buzzing in the tank?
I took it into the dealer (Sewell Subaru in Dallas, which was a great experience BTW) and they confirmed that it must be the pump. It was removed/replaced and the noise has not returned.
I searched the forum and couldn't find anything about it, so I placed this here in hopes it could help someone else out if they have the same issue.