How did the team come to Privet Drive to get Harry out of there for the last time?

Question

At the beginning of the Deathly Hallows, a whole team (13 people) comes to Privet Drive to get Harry out of there for the last time.

Pausing only to employ a few of Uncle Vernon’s choicest swear words, he staggered back into the kitchen, clutching his head and staring out of the window into the back garden.
The darkness seemed to be rippling, the air itself quivering. Then, one by one, figures began to pop into sight as their Disillusionment Charms lifted. Dominating the scene was Hagrid, wearing a helmet and goggles and sitting astride an enormous motorbike with a black sidecar attached. All around him other people were dismounting from brooms and, in two cases, skeletal, black winged horses.
(DH, Chapter 4, The seven Potters)

So they came flying brooms, Thestrals, and the giant motorbike, protected by Disillusionment charms.

But the Disillusionment charm is not completely effective, it does not let people become really invisible, just... less visible. (And the motorbike is kind of noisy.)

Harry looked down at his body, or rather, what had been his body, for it didn't look anything like his any more. It was not invisible; it had simply taken on the exact colour and texture of the kitchen unit behind him. He seemed to have become a human chameleon.
(OOTP, Chapter 3, The Advance Guard, just after Moody disillusionned Harry)

How (on their way to Privet Drive's garden) did they went unnoticed through the bunch of Death Eaters that was strolling above the vicinity?
(I can't believe the Death Eaters arrived after the team landed, their info was that the move-out was planned for the nightfall, and they probably were there in advance)

Answer 1

They didn't necessarily need to go unnoticed by the Death Eaters. The Death Eaters simply had to go unnoticed by them.

The Death Eaters were there for Harry specifically, not the Order as a whole, and they needed the Order members to bring Harry outside of the protection of Privet Drive in order to move him before they could harm him. They're not going to risk blowing their cover - and losing the element of surprise when Harry is vulnerable - to get some easy kills on Order members. Killing, or at least harming, members of the Order once the fight started would simply be considered an added bonus.

The Order, for their part, were under the impression that Voldemort and his followers didn't know their plans, so they had no reason to suspect that there was a large group of Death Eaters hiding in the vicinity.

I see no reason to think that they didn't simply fly. I think we can rule out a Portkey for the same reasons one couldn't be used to transport Harry out. Apparition may have been an option to avoid having to fly the entire distance, assuming that a half-giant like Hagrid can Side-Along Apparate.

Answer 2

While disillusionment charms in general are not entire invisibility strong wizards (Dumbledore for example) can turn invisible using disillusionment charms. While the Order do not have wizards of this strength in DH they have many powerful witches and wizards with them so the disillusionment charms will be very good and hard to see through. On top of this it is dark which makes it difficult to see the Order even without charms. On the noise issue there are certain charms that can prevent others hearing sound you create. I think they use one while planning to find Horcruxes at the Burrow.