Chirp noise in drive belt area - 2011 E350
 

Anybody got any ideas on this? There may be a clue around 1:30 when I have the camera on the belt tensioner, as you can see it moving in sync with the squeak, but I am not sure.

Here's the video

It's a common M272 problem. Either pulleys or tensioner are bad. I'd just do all of it. FCPeuro has a kit and they have a lifetime warranty. Strangely rockauto had a kit for the W211 but not the W212 although it's the same parts but the belt is slightly different but not by a lot. I've also replaced the thermostat as you normally have to take off the pulley anyway to do the thermostat. They also have a good price on the thermostat and everything they sell has a lifetime warranty. When replacing the pulleys make sure you keep track of the parts, I think there's a washer behind one of them but not the other.

https://www.fcpeuro.com/products/mer...-272273beltkt1

https://www.fcpeuro.com/products/mer...-4834100d#desc

A chirp like that is almost always a bearing getting dry. On older cars is was almost always the water pump getting ready to fail, but on this engine I would put the highest odds on the tensioner. I'd try that first before going into more pulley or accessory surgery.

Yup as mentioned above - 90% chance it is a Pulley -
If you are frugal - you can pop off the belt (via the tensioner) and then you can spin by hand the 3 pulleys - if they roll smooth like butter - they are most likely good - if they rattle - then there is your problem..
I had one bad pulley and that is how I found it, it was the cheaper $35 pulley that was bad. Most dealers will have those in stock as well as aftermarket stores...
(maybe good time to replace the belt if not frugal too LOL)

Cheers
JPC

When I did mine, one of them was bad, but the other ones weren't too far behind, not smooth like the new ones so while you're in there, you mind as well do both pulleys and the tensioner.

Ill bet you have a lot more room to get in there with the V6, the V8 is SOOO TIGHT...there are some advantages to having a V6...(I'd rather have the tight space LOL)

Thanks for all the replies and advice. I ordered both pullies and the tensioner and will put them on this week sometime. I took it out for a drive yesterday and it was really loud. I replaced the belt when I did my engine mounts, so that is still new and will reuse. I got everything from fcp euro out the door under $100 and should be pretty straightforward to replace them.