can't figure out

I have a 2002 Monte Carlo SS and lately it has been acting up and I can't figure out whats going on. I'll be driving down the road and it'll start chugging a little bit and making this awful noise. The check engine light will start flashing at me. Most of the time when I stop though, it quits making the noise or it'll quit before I get to a stop and then run just fine.

I've put the code reader on it and it never comes back with a code. I managed to use my cell phone and take a video (for the sound, and use the light to see if I could see where it was coming from) but I can't even tell where it's coming from.

I have just recently replaced the water pump. It had done it once before then, so I'm not thinking it's a bad water pump. I thought that maybe it was the idler pully, but had that looked at and it seems fine I guess. I've uploaded the video to youtube since I couldn't attach it on here, so here is the link... http://www.youtube.com/watch?v=bc7nucRCsGM Any help would be greatly appreciated. I can't/don't want to drive it much because I don't want to do more harm.

Thanks!

http://www.youtube.com/watch?v=bc7nucRCsGM

for some reason its mis firing. The flashing engine light means that your putting raw fuel into the cat causing damge to it. I would start with plugs and wires.

Flashing CEL means the engine has a current Misfire Condition.

Flashing CEL means the engine has a current Misfire Condition. what does CEL mean?

Check engine lite.

Hey, I'm sorry I never posted a reply on here, but I figured out the problem...it was a bad coil, after getting your posts about a misfire I checked them and one wasn't working. Thanks for the help and sorry it took me this long to post a reply.