I think there is more induction noise on the M104 engine, because it is a Dual-OverHead Cam with twice as many valves as the M103 engine.

In short, it breathes more, hence more induction noise.

If you think the M104 in 2.8L or 3.0L HFM sounds aggressive, you should try the AMG C36 M104 engine (3.6L).

I have the AMG C36 powertrain in my W124 wagon, and it has LOTS of induction noise, but it is VERY quick (3.07 diff).

:-) neil