I get the exact same noise (11WRX). It only seems to happen when the temp is below 32F (it has been in the single digits here in CO at night). I only hear the noise during the first few minutes of driving on a cold engine. I freaked out the first few times I heard it, but IMO it is normal. Honestly, it took me awhile to get used to all of the different noises this car makes lol.