The motor has obvious knock at low RPMS around 2k but its only truly audible with the stethoscope on it. The noise is audible outside of the car when its cold.
still could be piston slap. no reason for rod knock to improve or get quieter as the engine warms up.
if it is your only car and you NEED it to be operational buy an engine and do a swap. but if you can afford to wait until the engine fails to buy an engine, you MAY have a long wait.
i bought a 97 outback with noise and drove it 40k miles . at some point early on i realized it was piston slap.
the 99 ej22 is a phase 2 engine and it can have slap.
drive it until it gets worse.