It may be the serpentine belt. Sometimes when you purchase an "on the cheap side" serpentine belt, it has a tendency of making noise even when the tension pulley has been change. Try purchasing a more expensive belt. The diamond back serpentine belt may be the best solution for this problem.
You can change the serpentine belt by loosening the tensioner pulley. When the tensioner pulley is loose and the serpentine belt will become loose. Put the new serpentine belt on and tighten the tensioner pulley.
Valvoline Instant Oil Change offers transmission, radiator, gearbox, air filter, battery serpentine belt, air conditioning, fuel system, and gas saving services. They also offer tire rotation and drive thru oil changes.
Unlike serpentine belts where a spring tensioner makes the job difficult, Subaru uses v-belts and a long threaded rod to tension the belt. You have to remove the two pulley shrouds at the top to gain access to the belts and tensioners.