WTF - Late night road thumper

Originally posted on au.motorcycles:

Hello,

I've been lurking in this group since I posted my dirtbike for sale (http://forsale.rmwpublishing.net/ktm/) and seen that there are a lot of people "in the know" with what goes on on our roads. For those of you; answer me this.

Late last night (or really early this morning) I was woke by what sounded like a mechanical armed garbage truck. When I looked outside I saw a big black FBI looking GMC towing a large box-trailer with some flashing lights and some machinery on it. Driving down the middle of Seven Hills Road (NSW) this car would floor-it for 5 meters then wack on the brakes. When stopped there was a mechanical sound then a large thump (sounded like a big rod was been whacked on the road). This would happen twice before the car speed down the road another 5 metres. About 15 metres behind was an old 4x4 Mitsubishi wagon with a big flashing "move over" arrow to warn any other cars.

Both these vehicles did not seem to have any signage on them (RTA or otherwise) and I didn't get any info in the mail about it. Any ideas what this car was doing an who they work for?