The Holden Astra had many issues most of which are common knowledge, however there is one that comes with the rarer 2.2 litre engine that gets many people stumped. A squeak noise that sounds like a drive belt squeal can be heard at idle. Whenever the squeak occurs a slight dip in RPM occurs and many mechanics spend hundreds of ours replacing drive belts, and water pumps trying to rectify this fault.
The noise actually occurs at the rear of the engine when a car is raised on the noise sounds like its coming from around the rear main oil seal. Its not anything to do with the transmission either although many torque converters have ben replaced chasing this fault too.
The perpetrator of your irritating squeak is actually the PCV valve. Once the diaphragm inside the valve fails it causes this fault. Replace your PCV valve and your irritating squeak from your 2.2 Astra should be gone.