Improptu restarting of Macbook Pro while in Sleep Mode A week ago I bought a Macbook Pro Retina (mid 2014) version - and in the first few days of running it I have noticed about 4-5 times that the Macbook occasionally restarts itself - so far always in sleep mode. 

Even if the lid is closed, I can hear the opening chime when you restart a Mac.

I'm concerned that this is a hardware issue and one I'll have to go to Apple with, but I wanted to know if anyone else had this issue that they have already resolved, in case this is something that's due to software rather than hardware.

I don't believe there's a heat issue (I don't feel it running hot), and I don't believe there's a setting in 'System preferences' or similar that's causing this. Also, I haven't seen any note on the Macbook about a kernel panic.
This is almost always hardware. Each time this happens, when you notice it, run sudo sysdiagnose from terminal.app and keep track of the times. You might find some clues looking at the system.log in each case to narrow down what was happening before the failure.

Also, you can start the Apple service online - sometimes they offer to run a diagnostic remotely, but usually that's for iOS and not Mac, but it might not hurt to request info on what a hardware repair might look like and/or cost from Apple. See https://locate.apple.com for your options there.