Over the past week two weeks I have heard at least one or two snaps when just driving straight at about 20mph. Then the other night I had to drive through about a 15 foot long flooded, maybe at or just below the rocker panel / frame. I drove a mile or two under 40/mph after that and did not hear or feel a vibration. Then the other day, after about 1/2 mile and the car reaching 4th gear, I got a vibrating hum. I turned around to head home and check it out, flushed brake lines which was well overdue and checked brake cylinders to exclude brakes as the issue. It would still vibrate, hum once in 4th gear. I tried manual with the paddle shifter and then it began making the noise once in 3rd gear and after a couple stop and go's trying to figure when exactly it starts, it began almost but not exactly once in motion. I uploaded a video to YouTube with a view of the underside and with the sound while in gear. I haven't driven it much to fully test if there is any performance loss, but there does not seem to be from what I could tell. Also, I've recently started using sport mode I rarely ever used in the past and did notice some excessive winding of gears getting on the highway. If it was the tire rod (no slop in either wheel though) or inner CV axel I was going to order the part and attempt the repair, but was hoping that someone with more skill in auto repair to take a look and listen before I decide whether to attempt the repair or bring it into the shop and if a straightforward repair, let me know if any special tools or parts I might overlook are needed. Thanks.

2014 E350 W212 Buzzing Hum Vibration 169,000
0:00 Driver's Side CV Axel & Tire Rod Area
0:19 Transmission Underside Area
1:07 Audible Buzzing Hum With Moderate Vibration

 

At the 3 sec mark on your video it appears that the sway bar link bushing is compromised and leaking grease. This might be the cause of the sound you're experiencing. Imo I would definitely replace both links. Do a YT search for W212 MB sway bar link...plenty of videos walking you through the repair if you were to tackle it as a diy.

 

Thank you Raj. Not familiar with these type of repairs, the sound just seems constant and at a high revolution for such a low speed if that makes sense but I will give your advice a go, seems if I hang onto it, they should be changed either way (passenger side has similar grease but not splattered onto other parts in the wheel well).

 

Also check the cv boots both sides. The 3 sec mark also shows grease on the CV boot...unable to tell if it's grease splatter from the stabilizer link or seeping out of the cv boot. As to the sound on the video...I noticed you were turning the steering wheel when the sound occurs...have you checked your steering components? Check to see if you have the proper amount of power steering fluid in the reservoir and then check the steering rack underneath the vehicle for leaks. The vehicle definitely has to be on a car lift to for inspection.

 

It is electronic steering with no fluid to check. Rack failure was a concern and if any fluid was leaking from the system, I am not able to wrap my head around what fluid that would be at this point, though I certainly saw the same potential leak you do on the boot. I would also like to check the front differential fluid but there is no way to check it other than flush it and refill through the axel which I would like to avoid. I am considering back-filling through the drain if the sway bars does not fix the problem. They are absolutely loosey-goosey, full of play and need replacing. I will make my way through the front and rear suspension system shortly after this problem is corrected. Overdue and neglected, admittedly. Sucking in water through the tire/tie ride boot was a concern, but with no signs of failure, I am now planning on tightening wheel bearings when installing the sway bar linkage arms. No pun intended but if rotational play of the wheels are in your "wheelhouse" I have yet been able to come to an understanding if the play I have in both my front wheels is typical or not. I do agree that it could use a complete inspection with a lift and though I am confident my area MB dealership is well trained and knowledgeable, I pour all my liquidity back into inventory for a newer business I've started since relocating to middle America Kansas and have encountered incompetence with nearly every service I engage from non-dealership auto repair that actually broke electronic components of the car during my recent 5k vacuum leak whistle to system failure repair, to the negligence of jewelers not being able to identify natural gemstones to veterinarian unable to identify a life ending ailment for my fur companion. Sorry for being long worded, but due to the constraints of running a small business, if I can't fix this one myself, I don't want to pay what the competent dealership would likely charge based on past experience with Boston area service when running a more lucrative business where the car will have reached the end of its economic life for me and on to a 1993 pick-up truck until I sell some high ticket items sadly. Not meaning to drone on, but if this wheel slop/play does not seem excessive, it would save me the time of opening up the hubs to attempt the tighten. Either way, I do appreciate the time and input you have provided with prior posts. Thank you.

 

I just learned something. I did not realize that the W212 switched to electric steering in the middle of the model run.