1998 x308 (120,000 miles) was a daily driver by previous owner and has always ran smooth and sounded great. But after a long stay at a mechanics garage to fix a knuckle bearing the car has suddenly developed an odd noise. The previous owner replaced the secondary upper tensioners. I am hoping this isn't the rattle of the tension chain - the videos I have heard of other tension chain death rattles seem much louder and with many more other sounds.

Attached video of the sound - any thoughts or ideas ?

 

Hard to tell from my computer's audio, but I've also heard something like that from loose/dry bearings. If you've ever held a caged ball bearing in your hand and tried to spin it with no grease, and nothing to provide any pre-load, it can sound a bit like electrical static as it wobbles and the ***** rattle around. But which one? There are a bunch of them. Doesn't look like its the fans. Does it sound worse or go away if you change the rpm of the motor or switch on/off accessories like a/c, heat, headlights, etc.? Maybe the heater pump? My go-to for diagnosing noises is my mechanic's stethoscope. Touch it to various components, particularly near the bearings, and listen to pinpoint.

 

Water pump saying goodbye
To make sure spray some silicone on the pump itself spray good amount then start the car if noise gone it's the pump

 

Remove the serpentine belt and start the engine. It may be the idler or tensioner pulley

 

Sounds like a belt slipping over a locked drive: likely tensioner or water pump. Stethoscope

 

I’ve heard that noise many, many times. At quick glance, it seems at least your drive belt tensioner pulley is still the original plastic. You can replace just the belt tensioner pulley with the upgraded metal pulley. I’m pretty sure that the bolt going through that pulley gets turned *clockwise* to loosen and *counterclockwise* to tighten. Please look further into this before just taking my word for it. You can also replace the drive belt idler pulley (if it’s still the original plastic one) at the same time. I know for a fact that it’s the conventional righty tighty lefty loosey for just the idler. I don’t have the part numbers sorry.