I've got an engine-based whine that starts dead-on 2000rpm and continues to around just under 3000rpm, which equates to 55-60mph in 4th gear. If I let the revs drop off to under 2000 it disappears. Isn't there if I slip into neutral at 60mph, so rev/engine speed dependant. Cruising at 70mph, at 3000prm, all is quiet again.

I've had the belt off and checked all accessories/pulleys etc, nothing untoward, tensioner, alternator idler & fan pulley bracket all recent replacements (noise was there before all of these done), air/smog pump is removed.

Engine runs fine, no noise at idle, power good etc. Just that annoying whine.

The only thing I've read about that changes on the M104 at 2K is the VVT system, which is engaged at 2000rpm apparently- could that be noisy?

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1993 320TE M104
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past:

1983 230E W123 M102
1994 E300D S124 OM606 (x2)
1967 250SE W108 M129
1972 280se 3.5 W108 M116
1980 280SE W116 M110
1980 350SE W116 M116
1992 300E W124 M103
1994 E280 W124 M104
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"music and women I cannot but give way to, whatever my business" -Pepys