Flooding can happen by chance or be caused by leaking injectors, too much fuel pressure, or a bad ECT.
Is it still flooding?
It would be best if you could describe the noise better. Valve chatter at an idle is caused by thin oil, no oil pressure,or sticking valve train components. If the oil has now been changed, these don't make much sense. If the timing chain tensioner is stuck or damaged a clattering sound will come from the front cover only. Valve damage is possible depending on how they got it started.
If the oil was too thin with gas and the engine was run for any length of time, bearing surfaces could be destroyed. This would cause a deep hard knocking sound.
