Alright after a discussion with Pat and further investigation we figured out that the noise was the front drivers side piston hitting the threaded plugin the steam chest. This is not a good thing. Luckily we caught this issue immediately so it didn't cause major damage. We managed to tighten the piston back onto the rod and peen over the threads so hopefully this won't be happening again anytime soon.
This is not exactly the type of stuff I like to be doing two days prior to a big tour...
