03 WRX - 101k miles
1. only between 3k and 4k rpm.
2. only when the car is in gear - and never at a stop
3. only under acceleration, more so under partial throttle
It's most noticeable in 1st gear.
To describe the sound, just tap your fingernails on your computer desk at random and that's pretty close.
The car does not feel like it runs any differently since it began.
I'm really hoping it's something stupid like a heat shield, but I haven't had a chance to check! Thanks guys!