That is the timing chain guides you are hearing. They will need to be changed. It's a very involved job (read over $1000). Driveline vibration is most likely a U-joint at that age. There are two on the front driveshaft and one on the rear driveshaft.
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2007 Xterra S 4x4
Wheels, Tires, and Suspension
285-75 R16 BFG AT-KO, Pro-4X Wheels, 2" OME Lift
NXRocks Skids, TAG Rear Bumper, White-Knuckle Off-Road Rock Sliders
Xoskel Bumper Mount Bracket, Blacked out Emblems, Weathertech Vent Visors, FOURTREKS Hi-Lift Mount, Wilson1000 CB Antenna
Pioneer AVHP3200DVD, Midland CB, Compass Mirror, Nissan All-Weather Floor Mats, Nissan Carpeted Cargo Mat