With the ride hight.. Ie exhaust sitting to low, it will cost you but get an exhaust place to re run that section higher, if that is the only part making it lower then 100mm
as said before you just need to get it blue slipped
when your at the exhaust place get them to rite you a certificate (receipt) stating that it is x amount db, it will take them like 5 mins to test, they just have a sound meter tool
they should write you the cert if it is at thelegal limit, get this done before the blue slip so as you can show the joint where you get the blue slip done
I got done about a month ago in my wagon for exhaust (unbolted at diff and half unbolted at cat), low ride height (cut three coils out of rear springs) and pod filter (I had it in there jus cos I could and for the wank factor). But I got my blue slip done in bowral, country town so they were pritty leanient