strange noise

[Meatball]

Ive got a strange echo high pitch noise coming from the rad area?
It only makes this noise up to the fans kicking in?..weird!!

Could i have an air lock??..or an odd vibration.

[Ozstyle]

Hi,
I'd be thinking fan motor brushes or motor bearings on the way out.
Short out the otter switch wiring, turn on the ignition and then disconnect one fan at a time to isolate and see which one (if any) is making the noise.

Ozstyle