Originally Posted by GrumpyPitbull
This thread is a little confusing, but I get the impression that he has never messed with the tune, and found out it has a stock tune. So when he got the car, it had a stock tune with those mods on it. Then he drove it with the mods and stock tune for 6 months until he put the stock stuff back on.
So OP, what these guys are trying to tell you is that you drove your car with an improper tune. Depending on what tune your running, you were either messing the car up when you got it, or you are now that you put the stock stuff on it.
With the mods you have listed, that car should have been running a stage 2 tune when you bought it.
This is the way I took it, too. By all accounts, it sounds like you now have a stock tune on it. If Subaru says you do, then you do. They would know by the codes. The other lack of answers are unacceptable from various shops. I hope you didn't pay them for this crap.
As for the rattle, do the simple thing first and check that up pipe as described. It's simple and may be a quick fix. Unfortunately, with the odd hesitation you're getting, I'm fearful it's something much bigger and more expensive.
It sounds like you have a headache on your hands. Even if the rattle is the up pipe, the previous owner handed you a car with an improper tune. He was probably running an accessport he wanted to sell, so likely unmarried it and resold it. That, or he was running his setup with no tune for the mods at all. Either way, be prepared to spend some money or ditch the car. It certainly sounds like you should have got some more info prior to your purchase. Sorry man.