I recently got my rear discs and pads changed as there was a scraping noise (metal on metal I'm guessing) anyway, I only thought it was the pads, but was advised by the garage that the discs would need changing too as they were scored. So I agreed, and paid for the services. This was about a month ago. On my way into work earlier, I was hearing the same noises as before, but only coming from the the right rear side. I pulled up into works carpark and had a quick look, but it didn't seem like there was no pad left, but the top of the disc disk look scratched. Does anyone know what this could be? The car has probably done no more than 600ish miles (motorway) since they were changed. Am I within my rights to go back to the garage and get them to inspect it without any cost to me?

are the pads worn down or not? could be binding, sticky calliper/slider etc...

if you trust the garage then go back and ask them to have another look, if they've just changed the pads and not cleaned/greased anything that could be your problem.

hard to say about the discs without seeing them or a pic of them.

I wouldn't assume that the pads were worn down as they were new about a month ago...

Yes I agree with Mrhanky, go back to the garage. There is probably a caliper or slider problem they have missed on your first visit, a decent garage would not charge again to check this out. Good luck.

I agree seized calliper or sticking sliders
The brakes are not realising properly hence uneven wear

I've had the exact same problem, took the car back to the garage and he couldn't see anything wrong so he cleaned the brakes and fully lubricated them, for free. I have since got this noise back but not as bad. Could just be one of them things we have to live with, as long as the mechanic is happy that the brakes are in perfect working order then it's happy days with a really annoying noise lol.

There was a thread recently entitled "Noisy Brakes" or similar and a mechanic tracked it down to rust.I don't think you should ever consider any noise to be "just be one of them things we have to live with" as almost always noises are a symptom of a problem somewhere.
The old remedy was to turn the radio on high until the car gave up or worse.

To add on to Salmon's post, unfortunately it wasn't the rust that was the fault. The noise is still there

As for the OP, it's definitely best to have them checked out. Get a bit of Swarfega Stop Quick on the discs and see if it's any grease on the discs causing the noise. If that doesn't work, then check for uneven wear on the pads. Uneven wear is a dead giveaway of seized/seizing calipers.