I agree with Tactical; if the chain is rattling, it need replacement, and thickening the oil will not restore it to its former state, just maybe muffling the sounds. While I lack the knowledge that Johnny has with these engines, based on my observations, it seems that the noise often originates from the top chain, whilst the crank sprocket remains intact. I have seen two instances of vehicles that began to rattle after being still for many weeks. The upper chain guides were discovered to be fractured, and when kept stationary for an extended period, the oil pressure in the upper tensioner diminished, causing the guides to disintegrate. If the rattling results from the degradation of the guide rails, no additives or heavier oil can mitigate the noise, and the fragments of broken plastic guide rail will ultimately obstruct the oil pump's pickup gauze. Chains that break for the second time are often attributable to inadequate maintenance or, more commonly, the installation of inferior chain kits obtained from eBay. The mileage is contingent upon the treatment of the engine; a well maintained engine with 300,000 miles may be in superior condition compared to a neglected one with just 50,000 km. Conclusion of the essay!