Why would they make a squeaking noise when I apply the brakes, but only when Im going in reverse? It is very annoying. Funny thing is that it only happens when the discs are cold, not when they are warmed up. Any solutions? Get new pads maybe?

 

Its a very common problem. As pads wear down dirt/deposits build up on the pad surface and the trailing edge of the pads. When the discs are cold The disc surface has a tendency to "catch" the pads making noise in reverse. Doesn't mean there worn out. By removing the pads and using brake cleaner and 200 grit sandpaper, scuff up your pads and remove and round off the sharp edges all around the pads. Some pads (factory/oem) need this done more often than others(ceramic,carbon). This is a good time to check for wear, like deep worn grooves in the rotor. Don't forget to scuff up the rotor also. Good Luck

 

common issue that occurs when stupid brake places neglect to put the shims back on the brake pads when replacing them.

 

Can be worn too.
One of our cars would only squeal when in reverse but not a hint otherwise. It was in for some servicing and the service tech told us the rear pads were at the minimal level and needed to be changed. Usually I expect the pad wear indicators to squeal to let me know...but he was right...the pad wear indicator were worn but it didn't squeal.

Check where the noise is coming from to verify any possible wear issues.