I have a 04 MT WRX with about 80,000 miles and it is now making a strange sound. In neutral, it makes a fairly consistent knock at around 2,500 RPMs, give or take, after acceleration. So its not moving, blip on the throttle to about 4k and while falling, in neutral, it makes a knock. The engine was relatively cold when this happened. Any thoughts? Let me know if you need any further details as I don't know where to flesh out the details. Thanks!