It may be the heat shields on the exhaust system vibrating.
Subaru Outback was created in 1995.
The Subaru Outback is sold in the US.
The 2001 Subaru Outback has 16 valves.
The 2013 Subaru Outback has 16 valves.
The 2002 Subaru Outback has 16 valves.
The 2005 Subaru Outback has 16 valves.
The 2003 Subaru Outback has 16 valves.
The 2010 Subaru Outback has 16 valves.
The 2014 Subaru Outback has 16 valves.
The 2004 Subaru Outback has 16 valves.
The 2012 Subaru Outback has 16 valves.
The 2006 Subaru Outback has 16 valves.