Yeah, no one else can believe it too. There is a connection, once you put it in drive, the engine is connected to the transmission. No vibration with the car just in park. I'm not the only one with the problem, several other people have reported it and in each thread someone always says that they don't believe it's the axle, but it happens the same every time, new aftermarket axle, vibration right afterwards. I'm not sure how you think the mounts could get damaged too, they're nowhere near the axle. I've taken the front apart to do a few other things too like springs/struts, tie rods, ball joints, sway bar links, upper/lower control arms and never had an issue with the mounts. They don't last long to begin with.

In park there isn't as much of a load on the engine as in drive or reverse with the brake on. The latter exacerbates bad mounts, which like you said have short lives on these cars. I said highly unlikely with respect damaging the mounts... anything is possible depending on how someone chooses to perform the work.

That said, certainly an interesting experience... will keep in mind.

wanted to update -- on my personal car, the GKN axle didn't fix my chassis vibration at idle...I'm tempted to pull the OE axle apart and try to reverse the tripod bearing and then swap it back in.
I'm certain all my vibration at idle issues began RIGHT after the shop rebooted my axle and its all related. With the fact theres been so many people with the same issue, I'm not convinced the GKN axle isn't still vibrating.

I changed out all of the front suspension on mine, it turned out to be the motor mounts which was kind of a tricky job but doable

It is absolutely the cv axle, even though it's not spinning. I had mine replaced, and got vibration at idle. It felt like a classic motor mount vibration, but it wasn't. The solution is to re-use the factory cv axle MOUNTED IN THE EXACT SAME ORIENTATION AS BEFORE REMOVAL - JUST CLEAN THE JOINT WELL AND REPLACE THE BOOT. I told my mechanic to do this, and no more vibration. NEVER REPLACE THE AXLE AND JOINT - JUST THE BOOT!

I wound up replacing the motor mounts also. it did help the vibrations, but they did not go away completely. The shop did not save my old axles, so I still have the non oem axles in. It's bearable, but not what it was.

On BW forum I documented my findings - the OE axle fixes the vibrations 100%. Confirmed and photos show there is a difference in the axles size diameter length from boot clamp and weight.

https://www.benzworld.org/threads/e350-4matic-vibration-at-idle-diagnosis-thread.3073922/#post-18206740

the driver side axle is about $700, passenger side $400. Just FYI.

so as long as you’re sure it started after the axle swap, money spent on a Genuine MB axle will absolutely fix it.

it’s crazy how smooth my car is now. I lived with the vibration for years and forgot how enjoyable the car was!

On the left is new aftermarket driver's ft half axle. On the right is GKN OEM rebuilt. Behind the splines, the collar is too long by a 1/4 in. The transfer case is hard bolted to the frame. That 1/4 in. butts the axle to the case with no play thus transferring engine/drivetrain vibration to the body. Plain and simple. OEM rebuilt fixed the problem. Thank you to this forum for finding my problem in minutes and I hope this helps.

Also, a good test for this, (assuming you just replaced axle and have a vibration) is to raise vehicle at oem jack point with tire off the ground to let suspension and axle stretch out and start car. If vibration is gone, then thats the problem.

I am having this exact same issue. Front axles were replaced this week (they said they were too damaged just to do the boots) and now there is a noticeable vibration when stopped in drive that brought me to this thread. I don’t notice the vibration in any other gear or speed. How much is this worth fighting and how could they fix anyway at this point? I went to a shop that supposedly used quality parts, and charged for it. But I also realize it’s a 14 year old car that I won’t keep forever, but it’s annoying nonetheless. Other than the annoyance, I assume it doesn’t pose any safety or operational issue? Any thoughts welcome. Thank you!

I got a quote from a different shop after I got the axles replaced, and if I recall it was 3k for original MB axles. Wasn't worth it to me..... I thought of going to a junk yard and getting OEM axles out of one.

The inner boots on my CV axles went and the aftermarket inner boot kit was no good, couldn't get them to work. Ended up getting GSP axles on Rockauto and they ended being fine. The vibration doesn't really do anything, just annoying. I drove around with the replacement axle that vibrated for about a year til I got around to fixing the old mb axle and swapping it out.