I got a stock 04 wrx.the 2.0l turbo charged engine. I bought it when it had just under 50,000 miles, I've had it for a year now and it now has 64,000 on it and recently whenever I turn off the car after I've been driving for a while, it sounds like marbles bouncing around in the engine and this lasts for about 5 min after the car is turned off, also it doesn't Accelerate as good as it used to, I'm aware of turbo lag it's not that. Could this be a spark plug issue ? Detonation ? MAF sensor ? Idk help please. I'm new to the whole car scene. So I'm still learning.