What you said
I have a "settling time" challenge for my Year 7s (P7s) and 8s (S1s). I time them from the moment I let them in to the moment they sit down in silence with their equipment out. I record the times and add them up every half-term. The class with the lowest average time score wins; they each earn a credit and a sweet, and I emphasise the importance of teamwork in achieving a good score. This depends on pupils fully appreciating this aspect, but also having a reward that they want to work for.
For noise during the activity, there is a great resource on the TES website with Super Mario lives that get taken away when the noise level creeps up. If they run out of lives, they have to work on their own, in silence.
The expert view
Year 9s are a beauty, aren't they? This is very common, don't worry. Treat yourself to a reboot. Next lesson, give them your rules and emphasise anything they aren't doing properly. They will probably make a fuss about it. Make the consequences clear if they don't keep to the boundaries.
Then, start taking names of every pupil who transgresses. The question you should ask yourself is: "Has pupil X behaved as I asked them to?" If not, detain them. Avoid the "it's not fair" comments by keeping back every single one who failed to do as you asked. That might be most of them.
Repeat, repeat, lesson after lesson. You wear them down eventually. This is, I might add, a tiring strategy for you too. Make a big deal about lesson starts, for example, and then proceed as above. Yes, there are loads of issues, but the solution cuts through them all.
Tom Bennett is author of The Behaviour Guru; Not Quite a Teacher; and Teacher, published by Continuum.