Hi
Had a very odd problem last night on my 07 FL2.

When I arrived at home I turned off the engine, got out and locked the doors, walked away and then decided I would move it onto my drive, got back in and when I put the fob into the dash it sounded odd, a bit weak, I then hit the starter and all the lights went out and it made a groaning sound and nothing else happened, I tried it a few times but the same, I locked the doors whilst in the car, and then unlocked them again, but still the same problem.

I then got out, looked the doors, waited 30 secs, then got back in and it started just fine with no problems at all.

WTF?

Any ideas what could have caused this?

There was a software upgrade that sorted out problems similar to this. Does your trip computer reset on its own? If it is this, it's normally half hour labour charge at the main dealers.

no not had that problem.

Every now and then the music system will turn on but no sound (happened about 3 times in 2 years).

I would check the earth strap from battery too body ! may look perfect but check to see if its corroded internally.
May be by feel you will find it feels crunchy or peel back some of the insulation to check if its green !
or carry out voltage checks with a volt meter between engine block and battery earth terminal. Get someone to start the vehicle and when it cranks you should have zero volts ! 0.03 max. If you register over 1 volts or 3.7 in my case then you simply have a bad earth.

I had huge amount of issues for 3 years whilst under warranty and the dealer failed to find the cause until I fitted an extra earth strap. ( One of the many issues was the radio coming on of its own accord ! I was assured 100% this couldn't happen ! )
Just a couple of other symptoms was wiper doing a single random sweep on a dry screen when hitting the start button ! Random non start. windows with a mind of their own ! Auto lights & wipers were lazy ! to name just a few ! Jaguar x-type sport gone
Jaguar x-type 2.2d sport one of my best cars ever sadly gone
Freelander 2 GS auto 2008 most unreliable ever ! gladly gone
Freelander 2 GS manual 2013 only time will tell !