Engine light on, engine knocking 2004 6cyl Sonnata

knocking or clanging usually means engine rebuild or replacement
What is piston rod knock Engine Knocking Yahoo Video Search Results 3 Causes of Engine Knock

loose timing chain

I would go with the engine being bad.
A knock sensor only sends a signal to the engine computer when there is a vibration or noise like a spark knock. The computer then adjusts spark timing to compensate.
If the engine is knocking such as a bearing knock, the sensor will be activated.

It could be a loose heat shield on the exhaust system.They can sometimes come loose and rattle like crazy while idling.

this can be a serious problem, sounds like one of your engine valves, has the car overheated recently? if your valves bent, you need to take the engine apart hope i helped

Here's what you don't want to hear...A loud knocking noise from inside your engine is generally caused by a crank or rod bearing...when caught very early, sometimes they can be replaced. however, once the noise is loud, the attending crankshaft journal gets "hammered" out of shape and the job becomes very expensive and in most cases more costly than engine replacement. There is one other item that can cause a loud knock...your flywheel. Bearing problems generally cause low oil pressure. If you have that, it's gone...if not, have the flywheel checked before sending the engine to the scrapyard.

It sound like you dropped valve seat on the head. Did you recently over heat your engine .

how is the oil level and pressure?, how many miles on engine? is this a loud knock or rather a clatter/ticking noise? knock is engine rod or crankshaft bearings, clatter loud ticking is valve follower noise. how long before it (the noise) goes away?

big end or main bearing.

ok did the knocking noise speed up as you pressed the pedal? if so id check the oil first and see if that helps at all and if it continues to make the knockin sound you might have a thrown rod/piston. The oil can effect the the pistons being as it is the lubricant for the pistons to move up and down in the bores(cylinders) but the low oil would only cause the engine to start knocking if there hasnt been any oil added as needed for a long while. has you engine got hot or warmer than usual? the could also be a symptom of low oil.