Engine ping/knock?

Upon starting up my KZ650 today and got it to idle without dying, I noticed a slap/ping going on. Just got this bike a few days ago and cleared the tank of the old gas that was left in the tank from old owner, and put in fresh gas with a few cap-fulls of seafoam to help with the gunk in the carbs. I also have a new battery charged up and installed, and all electronics seem to be working fine. Once running the bike can't be revved past ~2-3k rpm and takes several seconds to get there with full throttle open. I am assuming this to be due to the carbs needing to be cleaned and possibly synched which I plan to crack into this weekend.

My question is, is the ping/knock likely due to poor idling from dirty/out of synch carbs, or is there possibly something worse going on inside? The sound seems to be coming from the front of the engine near the exhaust headers, and likely towards the center of the engine as well. When I get another moment, I will step out and try to pinpoint closer using the screwdriver to ear method. I took a quick video to help in identifying the sound which can be found here:

drive.google.com/open?id=0BzNZ4EjHjtH0RWphWjFfNzJtMTA

Thanks for any help!

sounds like an exhaust leak from where the downpipes connect to the cylinder head,

YUP
Steve

So I just ran out and started up the bike and sure enough you guys were correct. I felt around with my hand and found a small exhaust leak on 2nd cylinder (from front left) down pipe as stated. I have attached an image of above and below the section where the leak is. It looks like there's a flange or metal on the the cylinder head bent which seems to be the source of the leak from feel. Is this something that can be replaced or bent back, or any other quick fixes in this case?

drive.google.com/open?id=0BzNZ4EjHjtH0QkdMN0dnX0xhUjA

drive.google.com/open?id=0BzNZ4EjHjtH0TGdwMGg5NnRzUlU

#2 looks loose.
Steve