It's probably quite possible you have something different installed, 'cos I can't say mine is deafening in volume at that speed. But the sound is fantastic that's for sure. Although once I have the engine going past 4000-5000 RPM it starts to get loud - but this is a good thing, because of the sound.
It starts coming in about 70, then 80 you hear it, then it just BRRRRRRRR's
I'll have to try and record it
What does your's sound like?
Hmm...bit hard to say after driving the 350 so much lately...but I'd say it sounds much the same as what you describe, perhaps only alot quieter? If I've got the radio going, the engine is only really audible once the revs start to really come on (i.e that twin cam roar that sounds so awesome)
My tacho doesn't work in my 280 so unfortunately I can't say what revs exactly.
I just love the sound of my M110. It sounds like a well-calibrated and well-oiled industrial sewing machine; it idles very smoothly (noticeably smoother than two friends' W124 300Es with far fewer Ks on their clocks) and winds up respectably enough. Once it reaches about 85 km/h (no tacho - yet - in Boris) it takes on another life and pulls away from any vehicle I want behind me; it eats hills, chews them up, and spits them out like they were the slightest inclines.
A friend who owns a 5-litre V8 WB Holden ute was gobsmacked when he took Boris for a drive; his old WB (running on gas and petrol) was utterly gutless by comparison, though both cars had similar Ks on the clock (300,000).
Wow, I think my half-a-million km 280 might be a tad more worn than I thought...it goes well, but it doesn't sound like that description! Then again it does need it's injectors sorting out.