Mystery 306 Squeak/Whistle

I've had a 306 1.9TD Estate for over a year.

Every now and then a high piched whistling sound appears, sometimes a steady
tone, sometimes with an oscillating modulation.

I can drive for weeks or even months in silence, then the sound appears
again, maybe for just a few minutes, occasionally for hours. It seems to be
affected (on or off) in an unpredictable vague kind of way by steering and
braking.

My initial thoughts were that it was disc brake squeal. This theory went
out of the window when I came to a halt at traffic lights and the sound
continued.

As it is virtually impossible to induce the sound deliberately, particularly
when stationary, I've not been able to locate its source. I *think* it's
coming from behind the dashboard rather than under the bonnet, but I can't
be sure.

The sound appears whether or not the a/c or blower motor is on or off, and
the auxiliary belt appears adequately taut and undamaged.

Any ideas anyone, either as to the cause or bright ideas for diagnosis?

Peter

 

Remove the blower motor fuse to see if it is that.to me that what it sounds like. my 405 has the same problem the fan runs on its own even when the switch i turned off.goodluck
from chris Addlestone Surrey

 

Thanks Chris, I'll try that. Because the onset of the noise is so
unpredictable and can disappear for weeks, I'll try tying a length of string
to the fuse (F21?) so I can give it a tug when the noise appears.

I assume the motor bearing is the suspect?

Peter

 

I had a 405 TD and heard a similar noise from time to time. From my checks,
I concluded that it was the aux belt idler pulley bearing, the one which is
spring loaded at the top between the alternator and steering pump. However,
it was still the same a few tens of thousands of miles later, and is still
going strong with its new owner (my neice).

 

Thinking about it, Chris is probably closer to the mark than I am. The
bearings in the heater fan do dry out, and can squeal. If you can get to it,
a drop of oil in the right place could cure it.
The other motor in thesystem, at least on mine, was the little air temp
sensor fan which is behind a very small grill (about an inch square) to the
left of centre (I think). This is running more or less all the time if it is
on your model, and again the bearings can dry out.