Intakes are loud. A new filter will not help. If you want it quiet I would go back to stock. Exhaust's are loud too...probably should keep that stock.
4500rpm is about when those intakes really provide power and it's just the suction side of the engine you are hearing. Nothing is wrong.
Seriously though, a new filter will not help and the mechanic is trying to rip you off.
Autolite 103's, Cosworth CAI, FRPP Suspension, Strut Bars, DIY Short Shifter, SVT Air Dam, BSD, Poly Trans Mount, Borla 2.5", Roush Wheels, Tune...