noise from the intake would more than likley be injector tap or worse an air leak (you would notice sh***y running though), my s1 injectors are quite loud but they have been reco'd, use you screwdriver trick on the injectors and you will see what im talking about, to listen for an air leak, i use a piece of vacum hose stuck in my ear one end and point it around the intake gasket you will be suprised at what you can hear doing this, the noise at the back of the tapper cover could be a sticky lifter maybe, run some nulon lifter free through it next oil change and see how it goes!!