It will be the pipes behind the brake booster. they touch the fire wall and flutter under load.
Nissan have a fix for it or just put some packing behind them and it will stop the noise. Its all to do with the torque the engine produces...
Nissan also did mods to clutch and break lines but still terrible also rattle behind dash when I fixed my cd player fond wiring harnis flapping round in breeze wraped in spoge rubber 1 less rattle