06 subaru impreza knocking noise after it warms up?

[shooter]

i 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 doesn't 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