Toyota Repair: Engine noise during cold start, piston slap, cycl

Question
I own a 1998 Toyota 4 cycl camry and mileage is about 108K. Owned the car for about 1 yr and no problems till recently. During cold starts in the morning a loud knocking noise can be heard coming from the engine but goes away once the engine is warm, I have heard someone mention it could possibly be piston slap. Is that possible cause and is it serious if not attended to? Also my engine only goes to 1200rpm during cold starts, is that the norm?

Answer
Yes it could be a piston noise and yes, it can be serious and eventually cause engine damage, any abnormal engine noise means that there is excessive wear which will only get worse because the engine oil lubricating ability is reduced and there may be metal transfer from one component to another.