Well, I ended up not taking the car back to the place I had it done at. Had recommendations from 3 of my mates to head to a new shop. Ended up heading to the new place, had it up on the hoist for 20 seconds and told me it was an incredibly dodgy job in the first place.

He replaced the head studs with longer, alloy rod and used self locking bolts with loctite. Welded up the rear muffler connect, as the previous place had simply made a slip joint, tack welded it and threw a shitty clamp to tighten it, which didn't work and was still leaking. Replaced the cat bolts with spring bolts and nuts/washers as they were just normal 2 inch bolts and welded another leak that was found. Apparently the hangers were only tack welded on as well, so he did them properly and pulled the system down as much as he could as it was scraping on my rear bar and may have melted it in the future. Also discovered a over bend in the back pipe, in which they'd simply bent it back into place. Bloody nightmare come true.

Pretty ****ing pissed about the first job though, I'll be heading in there and giving 'em an earful about it, and have a few words to the guy who actually installed the system.

Cheers for the input, didn't expect this much of a headache from a exhaust upgrade D= !