2006 Chevy Equinox AWD
Most common is the serpentine belt tensioner units, when they get weak they can have a rattling sound and it won't be long before they break, sometimes if you look at them while the engine is running you can actually see them chattering and a with mechanics steathascope you can hear them. Other problems could be power steering pumps and or cracked pulleys, even some internal engine componets can have a rattling noise, so I would get it checked quickly, this has the potential of leaving you stranded.
We had that with our 07 turned out to be the bearings in the alternator
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