I feel the need to clear things up for everyone who owns a 4th generation minivan. If you have the 3.3L or the 3.8L V6 then please read on. On your alternator there is something called an alternator decoupler. It is a clutch and spring mechanism inside the alternator pulley. This device is used to absorb vibration within the belt drive system. When the alternator decoupler fails, you may hear a buzz noise on shut down, or the alternator will fail to charge(due to the clutch being broken inside) or your belt tensioner may exibit excessive movement.
What you need to know.... is that many big box stores are selling alternators with an inferior "simple clutch pulley" or a solid pulley on the alternator. There are two distintly different kinds of these "Clutch pulleys". One has the internal spring (Litens) and all the others do not. Make sure that if you ever decide to change the entire alternator for whatever reason, MAKE SURE IT HAS THE RIGHT PULLEY ON IT. The right one being a Litens Isolating Decoupler pulley and not just a "simple one way clutch". Simple one way clutches have only 50% of the function of the Litens IDP. These two pulleys are not internchangeable. Your belt drive has been designed with a Litens IDP for a reason. Don't buy an alternator with an inferior (lower cost) pulley.
I have read in these forums (an others) where people have changed their alternator pulley from a Litens IDP (OE) to a simple one way clutch. They did this either to save a bit of money or lack of knowledge about what pulley the vehicle required. Once this happens, people can't seem to understand why the vehicle's belt sometimes falls off, or why the belt tensioner keeps wearing out, or why the bearings in the waterpump keep failing. It is because the belt drive was designed with the Litens IDP and not the lower cost and lower function of the simple one way clutch. The Litens IDP is not hard to change and is currently available in the aftermarket. You can purchase the aftermarket version from www.iat-usa.com or if you want to pay more for the same part (OE) you can buy it seperately from the $tealership. Both the aftermarket version and the dealership version are made by Litens and are of the exact same OE quality.
Bottom line is ... know what you are buying and don't settle for the wrong parts just because they are a couple of bucks cheaper. Spending a couple more bucks now to put the right part on your vehicle will save you money and headaches down the road. Installing the correct pulley on your alternator will make you belt, tensioner, idler pulleys, waterpump and alternator bearings last a lot longer. But don't take my word for it, research it for yourself!