l just got an 06 wrx and it has a knocking noise coming from the drivers side of the engine. im thinking its probably the notorious subaru piston slap but unsure. it does not start doing it until it starts to warm up and only does it below around 1500 rpm. im almost positive its not a lifter and know its not a rod knocking

35,000 miles

try a higher octane fuel.

what elevation are you at? because l live in fort collins co and my 4.6L 98 mustang GT had the same problem up here..when l switched it out of 85 octane to 87 octane it fixed the problem.stupid ford guy at the dealership told me that my head gasket was prob blown.shows what kind of training they have lol

l have a n 06 & hear a little ticking noise from around the alternator but have not been able to pin point the cause yet. Bu knocking, do u mean it is a lower toned sound? mine is a very fast, high pitched noise & l am positive it is not from inside the engine. Maybe the cold temps is effecting the oil, You could try a thinner oil. l switched to synthetic oil in the same 5/30 viscosity & noticed that the engine just runs smoother from cold to hot & l do not notice the noise as much from inside the car. Could try that the next tome. If u really r sure it is from inside the motor, u have tot rear it down to see whats going on.