[Andyman]

High compression alone shouldn't make your car louder. Maybe the engine would shake a little more. It should make the exhaust a little quieter because the gases would expand more in the cylinder before going into the exhaust pipe. That loud car probably had a high performace camshaft and muffler.

I couldn't tell you how Subarus work with high compression. In general it increases efficiency and power but could cause some knocking at low RPM and low intake vacuum (high throttle) if you don't do something else, like use high octane fuel or water injection.