Subtle knocking/tapping noise when fan on and car warming up

[nsk040]

With the car on but stopped and the fan on (AC can be on or off) I hear a very quiet knocking/tapping noise which isn't precisely rhythmic but seems to be every 5 seconds or so. It kinda sounds like someone is tapping the bottom of a steel cooking pot lightly with rubber hammer. I can also feel this "tap" slightly through the brake pedal (again, sitting in car stopped at idle with foot on brake). This goes away once this car is fully warmed up. It also stops immediately if I turn the fan off regardless of it the car is warmed up or not. Any thoughts on what this may be?

Thanks

[nsk040]

Any ideas?

[nsk040]

I had 2 of the power steering hoses replaced and the power steering system flushed. The knocking/tapping has gone away. Perhaps the two were connected.

[ELCID86]

Odd. Glad you got it sorted out. And I hope it stays gone.


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"ZHP is a garbage option anyway- just some cosmetic upgrades with a different cam and diff to claw back some of the performance lost fitting those hideous and heavy wheels. Any 330 with a 3.46 diff will smoke a ZHP every time. The whole Mafia thing reeks of childish behavior." - anonymous E46 fanatic

[nsk040]

The noise has returned - any ideas? It's gotten a bit cooler so that may explain why the noise is back, but I still don't know what the noise is in the first place.

[Oli77]

Its not your thoughout bearing? Does it go away when you push the clutch in (car running at idle)?

[nsk040]

Its not your thoughout bearing? Does it go away when you push the clutch in (car running at idle)?

Don't think it's drive train-related. It goes away once car is up to temp or when the fan is turned off. Clutch doesn't impact it.