SemperInMotu

Okay, I finally took video of the noise the engine is making.

It's a 2008 xD, with just under 113K on the odometer. I replaced the alternator and the serpentine belt about 15K ago, but this has been recent. I'm using synthetic 0W-20 for oil, and it's got plenty of that, and has been recently changed.

I don't know why it was suddenly *out* of oil one day, even though there are no stains in the driveway, it has plenty of coolant, it hasn't been driven hard, and I can't spot any leaks anywhere else.

From what I've read so far, an old cam chain tensioner or bearings on the pulley are the culprit, but for anyone who's dealt with this before, I'd appreciate the input. Thanks!

DAlex

Well, here are things you need to consider:
Belt tensioner
A/C loose shroud
Alternator bearing
Also, your low oil issue may've damaged the upper-end. You may also have an oil blockage, resulting in upper-end damage. So first check the externals for obvious bearing/shroud rattles. If you're lucky, you might not need an overhaul, but I'm betting that you need at least a head job....

62Fender

A budget alternator bearing can go in 15k miles or less. You can isolate the sound with a long screwdriver. (Be careful that hair and or jewelry are secured.) Carefully place the tip of the screwdriver on the alternator housing, at or near the bearing. Place your ear at the handle end of the screwdriver. If the alternator bearing is bad, you should hear the sound rattling up through the screwdriver.

If your water pump is accessible, you can check its bearing the same way. Same thing for the belt tensioner pulley, (although you may need a tube instead of the screwdriver.) A pvc pipe or cardboard tube only needs to be close to the noise source. It doesn't actually have to touch the source like the screwdriver does.

If it's upper end damage due to lack of oil, the rattle should be louder after removing the oil filler cap (while the car's running.) Be ready to quickly re cap the filler hole if oil tries to spew.