Hey guys,

I have a 96 E320 with the M104 engine and a 4 speed.
I have had a strange sound that is barely noticeable for a while and was hoping someone may have any ideas as to what it may be.

Here is the scenario. When I drive on the freeway at speeds at or over 80 MPH I hear a very faint sound. It almost sounds like a low frequency grumble. The thing is, when I lift off the gas it goes away. If I press on the gas the sound comes on again. I thought it was the tires so when I got a new set I listened and it's still there. There is no noticeable vibration but only sound.

I don't think it's the tires or balancing on them.
I replaced the transmission and front flex disc about a 4,000 miles ago and the sound was there before this too. Who knows maybe it was always there and I just didn't notice it.

Does anyone have any ideas?

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2010 W212 E350 Sport
1996 W210 E320 (220K miles)