there are 2 rubber screw stopers on the back of the hatch, unscrew them a bit. This will put more pressure between the hatch and the back pannel. Also check the plastic garnesh piece on top of the car. they are prove to vibrating. Tap it and if it makes a noise, put something under it to stop it.
It's likely the hatch as pointed out, and there are several ways to fix that:
1. Tighten the hatch down. Four 12mm nuts behind the dome light panel.
2. Unscrew the rubber stoppers on the hatch until they're only in about one half turn.
3. Wrap the U-latch in heavy gauge vinyl tape, it's more durable than electrical tape.
4. Remove the shim under the U-latch. Those screws are VERY tight though.
Other noises I can think of: If your car is lowered with an aftermarket exhaust, the piping can hit the lower control arm. Loose interior panels can also shake around a bit, but they will have a distinctive plasticky squeak.
wipe the rubber hatch weather strip down with some water and a little soap, then wipe some interior cleaner that is safe for rubber on it. That will take car of the rubbery squeaky noise from the hatch moving. electrical tape on the U-latch helps a lot too.