I find the build quality of mine to be very good. Very little noise which I easily muted by the extremely careful application of a little WD-40. Now it's silent. I did this with my 8700 nearly 6 months ago, and it's still nice and quiet.
However one must remember that the engineers and designers have many challenges to face in making the thousands of decisions that go into a device like this. In this case they are building a device to a certain set of specifications, one of which is weight. Then there is the choice of materials. Plastic has many benefits which include light weight durability and some flex. It's unavoidable. Therefore the noises are also unavoidable, all they can do is try to keep them to a minimum.
There is a lot more packed into the newer devices as compared to the older ones. All you have to do is take a 7290 that's taken apart, place it alongside an 8700 that is also apart. There is quite a difference. I've seen it.
When I put my new 8800 side by side (assembled) with my 8700 they are both nicely built with a small advantage to the 8800 as the gaps are closer and more even. The 8800 also has a nicer overall finish.