OK, so I was searching the Internet and found on Matrixowners.com that there is a known problem with noise coming from the serpentine belt tensioner that Toyota is aware of and they have TSB 2750 to fix it. The noise only occurs after driving for awhile and then if you come to a traffic light to stop you hear this building whining noise that lasts for about 6 or 7 seconds then goes away. Also, it is an intermittent problem, doesn't occur every time you stop after having driven for awhile. IF the noise occurs when driving, you can't hear it due to road noise etc. So I had the dealership perform the TSB (which took a bit of work to get them to do it) and the noise changed a bit, but is still there. Now, the noise lasts about 4 seconds and doesn't seem to build up in intensity as much, but still very noticeable. In my cynical mind I'm thinking they didn't even do the TSB, which is to replace the serpentine belt and tensioner, but I guess I should give them the benefit of the doubt. So I went back to the dealership after having heard the noise several times and took a technician for a test drive, and wouldn't you know it, the noise wouldn't occur during the 15 minutes he was in the vehicle. I'll have to try to record the noise I suppose and play it to him to get him to believe me.