I have a cable running along my basement ceiling. There is a cord connection (looks like an extension added to it) but where they connect is all metal (it looks like an AUX jack). There is slack in the cable and the metal connection point was on top of an HVAC duct and when I walked by it I heard like a white noise and it was sparking!! I'm freaked out and have no idea if this is dangerous and what would cause it to spark and I'm scared to touch that wire now. I moved it off the duct but now I have no idea what to do. Any answers would help.
Was the air handler running? Metal duct’s should be grounded but sometimes are not. I have seen metal trunk ducting build up large static charges. In one case it was about every 12 seconds there was a snap quite loud. The charge was building up and discharging to a water pipe.
The white noise could be the close proximity of the cable to the duct so the charge is building up quickly and discharging. This will be the case only if the air handler is running.
I would want to verify if it is static charges building that the duct gets grounded large static charges can hurt like &$%#.
If the charge is there without air flow I would be checking the electrical system (grounding, possible only ground the water pipe replaced with plastic) OR if there is a voltage on the cable. The cable should be grounded at an inter system bonding point but if the main ground has failed this could have a floating voltage.
If it's a Cable TV wire, it's harmless and very low voltage. Basically, nothing more than static electricity in the winter when you touch a door's knob. You can very simply and safely just wrap it in a few layers of tape to remedy the issue permanently.
If it's a wire you really don't know about, then GdD is right in having it addressed by an Electrician. Even doorbell wires can be a shock hazard you don't want introduced to duct-work or real plumbing.