Be careful... There is a specific torque setting that the bolts need to be done up to.. The reason for this is that you dont want to completely squash the rubber washer that sits below it. The rubber washer works as a buffer to allow the inlet plenum to sit flush with the gasket. If you over-tighten the bolt, then the plenum wont sit flat and flush. Once the rubber washers are deformed, you increase your risk of losing a seal with the gasket.
Get your hands on the service manual, it shows the torque settings for the bolts, and shows what parts should NOT be re-used when dismantling/reassembling the intake. The parts that should not be re-used are the plenum gasket, throttle body gasket, and the nine rubber washers (on the RB25DET).
Are you sure there is a leak there? The sound might just be induction noise? At idle, try dripping a small amount of water over joints in the intake. If there is a leak, you will see the water get sucked in, and the engine might skip a beat quickly. Dont use too much water obviously...