Yes amps have filters built into them but like I said a cap is a supplement. Also the nature of a battery is not to change it's charge fast be it charging or discharging, that's where a cap comes in. A cap is designed to charge and discharge quickly so when say a snare drum note comes along and the amp needs instant power the cap is there to supplement the battery so that there isn't a drop in voltage for that split second.we're not salesmen here...and the amp has circuitry to filter the noise. and whats faster than a battery strapped to the amp? if i got it for free, i'd sell it (without said salesman approach tho). if i was to install it, i'd try and have it make sense to the owner that it was unnecessary but i'd install it if they insisted.