hi there bud sounds like a big problem, from what you wrote id take it in, see a noise like that means trouble, plus coolant mixing never a good sign, blown head gasket maybe, as for the sound could be a bearing gone....
easy way to check would be drain oil check for copper pieces/shavings, thats bearings if not could be a head problem best is to get it checked.
if you no your way around the bike you could pull the sump n check, and check the valve clearance for a bent valve i hope this helps good luck
I learned to hard way when my car did this and kept cranking it to show people what it sounded like and made it worse. If your not mechanically inclined...dont try this repair yourself. If you like taking things apart and putting them back together..then maybe try it with a service manual. Bottom line.. cheaper to just buy another used motor from a wrecked gixxer and swap on the parts from the other bad motor.