Mine popped open a few times when I first got it. I found the latch was binding and not fully staying engaged. I put a couple drops of 3 in 1 oil on it, worked it a few times and it hasn't done it since.
As for the rattle, on mine the throttle cable was rattling against the inside of the hood (the black cable that goes across the top of the radiator over the engine and down by the air cleaner assembly to the injector block). On inspection, you could see where the cable was rubbing off the paint on the inside of the hood where it was hitting. I loosely put a tie wrap on the air intake hose and around the cable to keep it from rattling on the hood - loose being the key word here. Worked like a charm.
Gregg