Yeah they're quite loud (especially if you have a stock / quiet exhaust).
Given map reading is off, I would check the vacuum hose to the map sensor for cracks, including the canister that is in line with the map sensor and vacuum nipple on front of intake manifold. These commonly work themselves loose so check those and again check all vacuum hoses
I wouldn't see Subaru in my humble opinion. They know nothing and will conduct a bunch of frivolous and expensive tests at your expense.
Mick