Here's what happened: Borg Warner made the timing set on the VQ40DE. The chains are multi-links and during the process of stamping the links of the upper chains, the dies would start to wear and not properly stamp out the links, leaving a sharp edge on them. How much of a sharp edge would depend on how much wear was on the dies that was stamping out the links. The upper chains that had links that were not properly stamped would cut through the plastic tensioner "faces" (or "feet," depending on whose terminology you prefer). Eventually, the chains would cut through the upper tensioner face until it starts riding on the hardened steel tensioner plunger. While this wear is occurring, the "whining noise" will occur and gradually get louder. If left unrepaired, the upper timing chain could jump timing, resulting in potential damage to the valve train and/or pistons, cylinder head and even the block.
The issue affects 2005 through 2010 Pathfinders/Xterras/Frontiers with the VQ40DE engine. Whether it will happen or not, or at what mileage it may occur, really depends on what condition the links are on the upper chains. If the chain links were stamped properly, there shouldn't be a problem. If the links were stamped at a very late stage when the dies had considerable wear, the problem would occur at a very low mileage. This is why we see some failures occurring at relatively low mileage while other occur over 100,000 miles...and on some, there are no timing chain issues. On my 06 Pathfinder, the noise started at 80,000 miles; on my 2008 Pathfinder, the chains started making noise at 130,000 miles. In most cases, all that is really required is replacement of the upper timing chains and the tensioner faces of the upper chain tensioners (and necessary seals, sealant and fluids required to do the job). Primary chains stretch very little and the chain guides typically show little or no wear. However, when the engine has a lot of mileage on it, most will opt to replace the primary chain and tensioner, all of the chain guides, water pump and thermostat. Most would replace the upper tensioners, but, that requires removing the rear timing cover because there is no access to the upper tensioner bolts unless the rear cover is removed.
So, I guess the bottom line is unless the chain is making noise, don't worry about it until it does..."if" it ever does.
