Check and make sure the exhaust is bolted into the block to spec? I tried once but it seems to be a weird size.

That could cause some vibration strange sound issues.

 

I'm shooting in the dark as it is a weird problem... and I do know a fair bit about bike motors - I just finished completely rebuilding one in my shed. All things are related and messed up fueling in one cylinder can lead to messed up sounds. IF a cylinder is not working properly, it isn't making full power, and half of the problems can be ruled out by sparkplug colour and condition.

Slap - or pre-ignition will show up on the spark plug. Check this if you do not believe me:
http://www.totalmotorcycle.com/maint...sparkplugs.htm

So if the spark plugs are fine, and you say it is coming from the left, then you need to think a single cylinder. More likely in this case would be an exhaust stud because it would not affect fueling or spark plug colour if it were only a tiny rattle.

One other thing that makes an annoying noise like that is the old double walled exhaust pipes when they rusted the inside wall out. That's not the case with a F4.

The cam chain is on the right - same side as the clutch.

Have you tried using a mechanics stethoscope to isolate where the sound is coming from? That would isolate it top/bottom.

Also on the left side is the stator - and I suppose that could make noise - that would be bottom left of the motor... and would be high frequency. It also wouldn't affect performance outright, but I suppose could lead to low charging output if it were damaged in the magnets or one of the pickup coils was damaged.