Humming noises

[perpLexus#2]

Hi, friends, who can help

I am driving a LS 430 with a total of 235.000 km continuously serviced since the very first day.

Since about 5 months the engine makes a humming noise. Especially at speeds of around 53, 62 and 73 km/h. It is a low frequency noise which occurs only under load.

The car was in almost 3 (!!!) Lexus Forums for about 4 days and none of them was able to locate the origin of that noise.

The results so far:

The entire exhaust line is ok; no holes, no wrong air inlet or outlet.

No vibrations or other mechanical causes. Mufflers both renewed 8 months ago. Gasoline pump exchanged during the recall.

It seems that the noise comes from the center of the subsoil, but this could not be verified.

What could swing there? Resonance in the engine block area?

All manifolds are ok.

Intake port ok.

Could there be something more serious behind this?

Additionally I have slight vibrations at 1700 rpm in the steering wheel.

All LFs are convinced that it may not harm the engine and I should drive worrylessly. 

What are your opinions and who has any ideas?

Who can help, so I can drive silently again?

Thanks in advance.

perpLexus#2