Need wiring help.

I am having a hard time wiring my sub woofer. My amp sub woofer out seems to only make the sub have a strong constant HUM and i mean STRONG. The question is can i do this. I am running wires from from front main speaker to the sub like in a series. Is this damaging in anyway? The system seems to work fine right now but I am not sure if it last lasting effects.
you'll need to provide more info. What amp? what sub? exactly how have you connected it? Other gear too.

More info is needed to help.
Ground loop on subwoofer plug??
If the sub has speaker in and speaker out terminals then it is ok to connect the sub to the same speaker outputs on the amp that your stereo speakers are connected to. Some people find this better sounding than using a subwoofer input or line level inputs on the sub.
I have a yamaha dsp-A1 and i'm trying to hook up a Kef40B sub. I have 4 Kef 70's and a kef 200C for a center. I'm running them off a B&K 200.5 amp.