I would ask the previous owner if they made that particular noise and if you can't contact anyone I would inspect each disc with wheels off for debris and/or improper wear.
A lot of times people do not properly "bed" their brand new disc pads and end up with possibly warped discs or glossy pads.
If nothing else, get those pads out and pop in a fresh set, check the disc surface with a flat edge and try again.
Congrats on the GT3,,, but take ownership and get in there!
