98 Rav4 Engine Noise: Most Popular Causes

What might cause a rattling plastic sound somewhere in the vicinity of the front pulleys? This happens whether the engine is at idle or at an operating RPM. I cannot seem to pinpoint the origin and was hoping, for lack of a better term, that it was a popular occurance with this model. I thought that it may be timing belt/chain-related or possibly something related to the water pump. The sound is something that is loose, but confined to an area within. It's continuous and sometimes more severe after a period of idle. Is this engine an "interference" engine? -having the possibility of valves reaching piston tops if a timing belt/chain is "thrown?" I'm concerned that the timing belt/chain might be the culprit and fear the worst for the engine. Any suggestions are good suggestions, whether from personal experience or from professional know-how. Thank you for your help.

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i have a 97 and i get the same kind of noise, wondering if anyone's gotten back to you? the noise i have seems to be worse when it's cold and most of the time goes away when it's warmed up, does yours? any help would be greatly apreciated - thanks! :]