ok so i just got a 00 2.5rs last week and i went on a pretty long trip this weekend. about 180miles 1 way. so about 20 miles or so before i reach where im going i start hearing a sound kinda like quietly knocking on a piece of wood or something and it only happens between 2.5k rpm and 3.5k rpm and its louder when under load but also makes the same sound when passing through that rev range decellerating. but after reaching my hotel i parked the car and when i drove it again last night it was fine. and driving around today it was fine as well... untill i made the return trip and again right as i got back into my town its started making the noise again. so it seems its only happening after very long drives. anybody have this happen or have any clue what this could be?

Sounds like a clear case of engine knock - "louder under load..."

What happens if you use higher octance gas? Any mods?

only an exhaust which was on it when i got the car. im using 89 octane in it. ive heard knock before and its not nearly as loud or as metallic sounding as knock usually is. and when i say louder under load i mean thats really the only time you hear it while decelerating as it passes through that rev range if your really listening closely you can just barely hear it.

maybe it's an exhaust leak?

maybe it is a bit low on oil and only makes it when it is fully up to operating temps?

yeah it was low on oil, i work for a the dealership i bought it from and i hadnt checked the oil since it had been out on the lot(they are supposed to do a saftey check which includes oil change before it goes on the lot) but apperently they never had a chance to do it before i got the car. and it was only once the engine reached full operating temp but now ive filled up the oil and it still is making the noise. so if thats the case do you have an idea of what it is?

my favorite guess these days is the timing belt tensioner. do you ever get it when you first start the car and its cold?

if i do its not loud enough to notice from inside the car later tonight ill pop the hood and listen for it when i first start it up.