Intermittent noise on WRX

[GB]

I have a 2002 WRX Wagon with 15k miles. A few days ago, it started making a
noticeable knocking noise, only after a cold start and between 1.5k and 2.5k
RPM. It usually goes away when the car warms up. Has anybody experienced
anything similar?

 

[David & Caroline]

If it just started, it could be something as simple as a tank of bad gas
(maybe the station you last went to had the wrong grade in their tank - it
happens - the local news did a special on that out here one time, and it was
alarming how many stations were selling regular as premium...) - just the
same, I would bring it to the dealer and have them take a look (drop it off
the night before, so that they can listen right after a cold start when they
can look at it in the morning)