Re: Very Very Strange Noise on...
I'm not certain that this is it due to the fact you still hear it with the fan off but there is a fairly common problem with the heater unit on 155s, mine makes a horrendous noise, similar to what you're describing. Apparently the flap motor spindle in the black round heater unit is broken which causes the noise. The only way I find to get rid of it is turn the fan completely off and let the motion of the car through the air push some air out the vents, not a good solution in 30 degree temperatures here at the moment. Its changed over time too, once it only did it at high fan speeds and not at all on aircon settings, now its gotten so bad it does it all the time.
There is someone here who took the black unit apart and swapped the ends of the spindle over or something which fixed it. Try searching this forum. I've just been looking for a 2nd hand unit.