Problem with 3.2Q DSG brakes?

I had this same problem on my civic. It was the rear pads - they'd worn down so much that the metal was grinding off the discs and I had to replace pads and discs. Not saying that's what you have, but the symptoms were identical. Take off a wheel and have a look.

Might also just be a sticky handbrake?

Nah its the weather, the rain, cold etc makes the discs rust overnight, therefore the pads also stick to the discs & can cause a clonk noise aswell in morning when you move of when the wheel turns the discs which loosens the pads, then when driving after a while & braking on/off it clears the rust from overnight etc & also the high pitched noise is most likely where the pad has ground into the disc & metal to metal has caused a ridge in the disc from pads where it will squeal, both things perfectly normal & also common on most cars tbh

The squeal can be fixed by 3 things, 1st you can have the discs skimmed flat again so no ridge this removes noise, 2nd new discs & 3rd new pads, personally I'd do 1st as have done few times before & fixed issue, you could do 1st & pads to be sure, but check the disc/pads wear aswell.

But saying that its not something to worry about at all unless braking is failing or causing issues once driving.

Have you taken the wheel of to check anything as yet?

I still think its disc or pad related, bearing could be but seems strangely coincidence standing for while then starts, which indicates discs that stick, cant see disc warped which would make pad constantly grind, but check it out cause we cant do anything from here but speculate, but thats the common simple problems

Mine does this every time it's parked up for more than a few days. Got back from two weeks' skiing yesterday and I KNEW it was going to do it even before I got in at the airport.
A few minutes later (assuming you use the brakes in that time) and it's gone.