Engine noise only when heater fan on

[stu]

Hi all, my 130BHP TDI passat est circa 2004 intermittently emits a cross between a bearing grinding noise and a clunk about every 5 seconds.
It sounds like its coming from either the centre or nearside at the front of the engine, probably one of the ancillaries running off one of the belts.
Weird thing is that it stops when the heater fan is turned off.
Any ideas would be greatly appreciated.
thanks in advance

[caldirun]

Hi all, my 130BHP TDI passat est circa 2004 intermittently emits a cross between a bearing grinding noise and a clunk about every 5 seconds.
It sounds like its coming from either the centre or nearside at the front of the engine, probably one of the ancillaries running off one of the belts.
Weird thing is that it stops when the heater fan is turned off.
Any ideas would be greatly appreciated.
thanks in advance

Check the ancillary belt tensioner, the top bush wears and the pulley runs on the top of the tensioner cutting grooves in it. Not so weird with the heater, the belt drives the alternator, the alternator drives the fan, no fan low load, fan on, high load!

[stu]

Thanks Caldirun. makes total sense. I will check it out.

[Crasher]

Turn the heating system onto ECON from AUTO and if the noise stops, you have a problem with the A/C compressor or its drive.

[stu]

Thanks for the reply. It doesn't make any difference wether its on econ or auto. Only affected when fan on or off.

UPDATE -
Turns out it was the clutch mechanism on the alternator. OUCH £168+ vat for new one (alternator).
Also replaced tensioner as this looked like it was on its way out.
Thanks for the replies.