I.e a line running straight from the turbo to the wastegate actuator? That is just going to limit your boost to the wastegate spring pressure (~7psi) and may be a reasonable safety measure until you get everything sorted out.
I'm not sure about how the BCS was hooked up, but most people who know enough to run one do have a tune for it. You can find out if your car was tuned with the cable - download the map that is on the ECU and look at basic stuff like target boost, WGDC. Or upload it somewhere and we can look at it for you.
Edit - the way you have the line might make the wastegate flutter more (no harm, just noise), and may explain the sound you are hearing - don't count on it though and still check for det.