I have previously been critical of how much noisier HFM versions of the M104 I have driven were than the M103 in my '90 300TE. My M103 is quiet at all throttle openings and only becomes audible at very high engine speeds. My father has a '93 E320 coupe (W124) with the 3.2 M104. Even at small throttle openings it has what appears to be induction "growl". Under normal driving conditions this can be annoying. At wide throttle openings this becomes an enjoyable sound that matches the spirited performance (being an Aussie delivery it has the 5-speed auto and 3.69 diff). It is even possible to hear and feel the points where the inlet manifold resonance tuning and inlet cam timing changes. A '93 E280 sedan (W124) with the similar M104 that I once drove made similar noises.

On the weekend a friend asked me to test drive a '93 300TE 2.8 (aka 280TE) that he is considering purchasing. This car has the same 2.8 HFM M104 to the E280 and a very similar to that in the E320 yet sounded and felt almost the same as my '90 300TE. Absent was the growl of the other cars with the HFM M104. The switchover points in cam timing and manifold tuning were also not obvious.

What now puzzles me is what causes the noticeable difference. I had always assumed the extra noise of the HFM M104 to be due to the plastic inlet manifold and ducting and yet here is one that is almost as quiet as my M103. Is it due to the wagons having a very different rear muffler to that on the sedans and coupes (ie. exhaust noise rather than induction noise)? All cars in question have standard inlet and exhaust systems. All appear to be running well although the wagon I test drove on the weekend did have slightly hunting idle speed in neutral and the idle speed would drop low enough to become rough when slowing to a stop at which point it would then recover to the correct speed (what could be the cause of this?). Its performance was about on par with (although no better than) my 300TE which looking at the specs would seem about right (M103 = 135kW, 2.8 M104 = 145kW).

Can any owners or regular drivers of various W124s (M103 vs M104, sedan/coupe vs wagon) please describe their experiences of noise levels?

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.