Subwoofer hum

Hi there,

I've had a room plastered and so put cables in the walls for my 5.1 set up.

For the sub and centre, I've put those in a fireplace hole, having removed the fire.

The cables for those are close to both the electric cables and also a central heating pipe.

I've put RCA screw terminals onto the sub's speaker cable, which is 4mm cable.

The sub has a buzz when connected to this, but when wired without going through the wall (which looks untidy because of the cable) there is no hum.

I can't easily put a new cable in, but before I think about that, would a shielded sub RVA cable solve the hum?

Many thanks.

K.