i think that the singing sand dunes are in the kharrara reign, before you enter the desert make sure you let out some air from your tires cause there are sharp rocks out there.
I posted some pictures and information on my blog here:
Basically, well worth visiting, although you may not here singing at the moment due to humidity.
They're featured in Marhaba. Yes, it's a nice place, though prone to litter and, especially at weekends, guys racing in landcruisers. This also makes it a bit dodgy as a camp site.
They get their name from the fact that the sand makes a rather haunting, deep noise when you run or slide down them.
No facilities, so take water and shade. And take your litter home, please.
Final point. They'll seem easy to get to in daylight, but a lot trickier to get away from in the dark, if you're alone, or haven't been there before.