Noise coming from accessory drive on engine (with video)

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I've owned my Sierra for over 5 years and 145,000 miles. I do most my own maintenance and feel I'm pretty in tune with the truck. Lately I've noticed an abnormal noise coming from the engine bay. I'm not sure if it's due to cold weather or just happen to begin when cold weather started. I took this video immediately after a cold start in my garage. Temp was around 38°F so cool but not really that cold. From what I can tell the sounds appears to be coming from the very front of the engine around the accessory drive. It's a little more noticeable on the driver side compared to the passenger side. Belts are all original but the vacuum pump was replaced in March. Sounds doesn't appear to be coming from that anyways. I'm wondering if it might be the belt tensioner? Belts look good but might be about time to replace them anyways.

https://www.youtube.com/watch?v=7YigepzOKcw
 
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I have used them before to isolate such noises . You can even diagnose a noisy alternator to determine if the front or back bearing is the noisy one .

Check all the rotating accessories , including water pumps , A/C compressors , PS pump , idler & tensionre pulleys .
 
Update: Removed the serpentine belt. Water pump and alternator felt normal. The tensioner pulley spun freely but had a little bit a "gritty" feel to it and noticed felt some slop. I decided to pickup a new tensioner (and belt since I had it off). After installing it does seem to be a little quieter. Will have the truck outside for the next few nights. If I don't hear anything after a cold start I know the tensioner was the problem. Thanks for the help!
 
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