The turbo spooling sound should be something that you look forward to hearing, it means you are making HP. The weed whacker sound you described, are you referring to a gas weed whacker (WW) or an electric one? ( No BS I am serious) If you are referring to the sound an electric WW makes, which is a whistling sound, then that is definitely the turbo. If on the other hand you are referring to a gas powered WW then I would think more along the lines of that being an annoying exhaust noise, and if that is the case I would suggest that you attend a car show or an evo get together and listen to as many different brands/styles of exhaust systems as you can. I haven't got the experience with EVOs to tell you when, in your modding, the stock exhaust will become to restrictive. But from other automotive experiences, it eventually will.

Also STIs are turbo charged too.