How about in neutral?
The tachometer may possibly be out of calibration
When the engine is at 4000, does it sound like 4000 or does it sound as if it's about to blow up (which would sound more like 6000)
What is the idle speed? This also may be something that has been incorrectly adjusted as people who have idling issues sometimes like to raise the idle speed hoping the issues go away
Where abouts is the car? Try to film a video, or if you're local to Sydney bring it around for a look or road test