Annoying "chicka" sound coming from engine while idling
 

When I start the engine, I get a "Chicka" sound coming from the front of my engine with every revolution of the belt. I just bought a beautiful 2010 ML 350 with 72,000 miles that rides great, but this sound drives me nuts. It was on the lot for about a month and according to CarFox, was serviced regularly by the previous owner.
While in the process of buying the ML, I did listen to the engine, but The lot was right off a major highway so I did not really notice it then, but the next morning I started her up in my driveway, and "hear" it is! Its not very loud, but loud enough. I am tempted to spray some WD 40 on the front of the belt pulleys, should/ can I?
I have owned a 1996 E320 that was very quiet, so I assumed the ML350 would be the same. Nope!:confused:

Check to see if the belt is starting to ride off the edge of the tensioner pulley.

Will do! Thanks!

Check to see if the black levers attached to the front of your intake manifold are broken. Common issue with this generation of the 3.5L engine and super frustrating. Ours had a bit of a noise like you described and I didn't think much of it only to have my Mercedes indy mechanic find this issue I wouldn't have otherwise noticed. Hopefully that's not your issue. As preventative maintenance I replaced our idler and tensioner pulleys and serpentine belt on our 2011 when we bought it. Probably overkill but the bearings in the idler pulley in particular is known to go bad and disintegrate on you at a bad time. I probably did it too early but I had a bad experience in a W210 I owned that left me temporarily stranded. The WD40 approach is not a bad idea though.

If you don't know what I am talking about with respect to the broken intake manifold look for my prior posts for a thread on the subject or search this forum or Google. Good luck!

Thank you! Great advice. You guys are awesome!

Control the urge. WD40 is not a lubricant, regardless of all the BS about this on the Internet and from the manufacturer. It is a water displacement (WD) compound that contains some components that lubricate but are intended to protect from moisture, and attract dust and other bad things for bearings. Use a true lubricant instead. Besides, the pulleys have internal bearings.

What WD40 is good for is for spraying in the engine compartment in general to protect from corrosion. It can be easily removed with a power washer and reapplied, and works great for that purpose, especially in marine applications. Chemically, that is exactly what it was designed to do.

Good Looking out Flybd5. I found the can, and decided to get to it tomorrow, saw your post and will now take heed. I will get a non destructive lube and try that first. I will update all. Thanks guys!

Update: I took it a reputable MB Dealership and had it fully assessed. 5 stars all around, but to be sure, I had them replace 3 pulleys and lube the RV mirrors ($1,100. later) same damn noise, but was told it was normal. I love this truck for the ride, look and feel, but the engine noise somewhat gets on my nerves. I have to remember, its an SUV. My 1996 E 320 Luxury was made of heavier stock/metal and maybe thats why the engine is more quiet? Now seeking a 2007 E Class for a second car and cannot wait to (not) hear luxury again! What can I say, MB spoiled me! LOL. Thanks again guys!

Still got the noise? I wonder if you can take a video and show us the noise area.

Funny story... I once drove my dealer crazy on warranty because of a rattling noise inside the cabin that only came up at speed. Drove me crazy, and they had it in the shop twice for almost two weeks. They took apart the dash, put a lot of stuff in there to deaden any noises, checked stuff, pulled apart ducts. Nothing. Turns out... get this... it was the transponder for the toll roads, EZ-Pay or something like that. I had it on my front windshield and something inside was rattling. They never thought about checking that either... but in the process, they found out that the problems I had with the engine idling rough and pushing the car left and right a bit was not the BS story they told me about "brake springs". They checked and the head had a leak in one of the cylinders and they had to replace it. Also under warranty. LOL! :)