My 190E is not quite the smooth highway cruiser it used to be. There is a hum at highway speeds. It sounds like someone blowing air around the top of a beer bottle (like a flute). From my experience, the sound from a wheel bearing is slightly lower pitched. It is not a constant hum either. Even if you maintain a steady speed, the hum has volume fluctuations. It starts at around 100 km/h and at 110 km/h the noise starts to get less loud. At 120, you can still hear it a bit but not as much as 100. There is also a vibration that seems to appear at 130 kmh. The car used to be able to cruise at higher speeds with absolutely 0 vibrations.

Also note that:

-I replaced the 2 front wheel bearings. One was shot. The noise remains.
-The 2 rear wheel bearings don't have any play and don't seem to get hot after driving for a while.
-I tried to change the diff oil but the drain plug is stuck! I tried the impact on it and it won't bulge! But when you open the fill plug, oil comes out. So at least it has some oil in it...
-I also changed the driveshaft bearing and the carrier. The bearing was so-so but the rubber carrier was blown. The noise is still there. BUT I might have put the driveshaft back on with one spline off... I think I did it right, but not absolutely certain.

I plan on dropping the rear subframe when I put the car in storage in a month. Do the bearings, bushings, diff r&r, etc...

A speedo cable that's faulty can cause a hum and vibration. There no cure for it other than replacing it. it a relatively cheap and easy DIY fix.

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio

Really? Actually at certain speeds the gauge's needle bounces up and down. Where does it plug in? At the transmission?