Hey guys....right basically a couple days back my emissions light came on, at the time the engine sounded fine, then a couple days later the engine started making a prominent knocking sound on start up, but no constant...it sounded like it was adjusting something, then after about 30secs the knocking sound stops. 9 times out of ten the emission light stays on, however time to time it'll switch off. I've tried search on here, but no one has mentioned the specifics about only on start up ect....
I've read it could be a couple things? Cam follower, fly wheel or tensioners? Anyone help me? And is it a easy fix?