fuel pump?
 

hello all.. few days ago i started hearing a strange ticking from the back of the car when its on idle.. checked the exhaust to check its not moving and it was ok. now the sound is there when i drive as well but it become faster ticking. when i stop after a few minutes of hard driving it become more clear. i guess its coming from the left side. can it be the fuel pump? i recently added a K&N fuel filter and i guess i started hearing the sound after i installed it. the car is MY02 STI7