I removed a blank two-gang wall plate from my wall to see what was behind it. I found this:
What are these? Speaker wires? I'd love to cover this hole in the wall over with drywall, but I have a feeling people are going to tell me not to do that.
Those are speaker wires and, going by appearance and the transparent jacket, they might not be fire rated. Most transparent PVC jackets are not rated, some could be.
Check the black writing on the jacket (near your thumb in that picture).
As is often overseen, in wall wiring must have a CL/CP or FR fire rating. If the wire runs through an air return duct or an air return wall space, a.k.a. a "plenum", then a higher "plenum" rating is required.
If it is not rated, closing it up and not using it unfortunately does not resolve the non-compliance. Best if you can pull it out.
This may very well be an issue that would not pass inspection, but once discovered behind a wall is not serious enough to require remediation.
Here's an overview of the pertinent labeling:
In-Wall: Usually in reference to an "in-wall rated" cable which is designed to be installed inside a wall safely. Cables that are in-wall rated need to have a designation printed on the cable jacket showing exactly what its rating is. These ratings are generally flammability related. CL2 and CL3 are commonly seen on standard in wall rated cables such as HDMI cables or Audio Video cables. There are also higher rated designations such as CM, CMR and CMP. If a CL2 rated cable is required for an installation, a higher rated cable can always be used in its place.
CL2: This is a cable jacket fire resistance rating defined in Article 725 of the National Electric Code. It stands for "Class 2 Remote-Control, Signaling, and Power-Limited Circuits" cable, which indicates that the cable is suitable for in-wall installation and use for certain low-voltage applications. Examples of Class 2 circuits include burglar alarm cabling, intercom wiring, and speaker wire. The jacket is designed to protect against voltage surges of up to 150 volts. CL2 cables may be further classified as "CL2R" (Riser Rated) and CL2P (Plenum Rated). For a more detailed explanation of Riser and Plenum ratings, see "CMR" and "CMP" below.
CL3: CL3 stands for "Class 3" wire and is also defined in Article 725 of the National Electric Code. Broadly speaking, it mirrors the definitions of Class 2 wire, but the jacket is designed to protect against voltage spikes of up to 300 volts.
CMP: This is a cable jacket fire resistance rating defined in Article 800 of the National Electric Code. It stands for "Communications Multipurpose Cable, Plenum", which indicates that the cable is suitable for installation in a plenum space. Because air travels throughout a building via plenum spaces, it is critical that cables that are installed in such spaces not give off toxic smoke when they burn. Thus, plenum-rated cables are designed using materials that burn more cleanly and self-extinguish more easily. As the flammability requirements for Type CMP cables are stricter than Type CM and CMR cables, Type CMP cables can be used as a substitute in any area where CM and CMR would be required. Cables that are labeled "Type CMP" must pass a standardized flammability test and be certified by an accredited laboratory, such as Underwriters Laboratories (UL).
CMR: This is a cable jacket fire resistance rating defined in Article 800 of the National Electric Code. It stands for "Communications Multipurpose Cable, Riser", which indicates that the cable is suitable for use in a "riser" installation, meaning, it can be installed vertically between stories of a commercial building. The goal of a riser-rated cable is to be flame-retardant enough to prevent the spread of fire from one floor to another. In that respect, it is more flame-retardant (and consequently, more expensive) than type CM cable, although not as much as type CMP cable (see CM, CMP). As the flammability requirements for Type CMR cables are stricter than Type CM cables, Type CMR cables can be used as a substitute in any area where Type CM would be required. Cables that are labeled "Type CMR" must pass a standardized flammability test and be certified by an accredited laboratory, such as Underwriters Laboratories (UL).
This is an example of proper and legal in-wall speaker wire:
Yes, those are speaker wires. A number of comments have noted that they might be connected to power anyway, so checking thoroughly - either to find the other end, if possible, or at least using a non-contact voltage tester to make sure they are dead - is a good idea.
If there are no 120V or 240V wires involved, you can cover this up with drywall. But before doing that, you may want to trace out the speaker wires to see if the box, using the speaker wires to pull new wires, might be useful for ethernet or other wires.
Patching/painting is definitely an option. Painting the blank plate to match the wall color would be a lot less work, though if you are planning to paint the entire room soon then patch/paint makes more sense.
Your safest bet is to remove these wires before patching the hole. If these are indeed intended for speakers like they appear to be, then removing them shouldn't be too difficult.
These sorts of speaker connections are typically used for speakers that either mount high on the wall or recessed into the ceiling. If you have no speakers in those locations and don't see anything that might look like a cover for the other end of the wires, there are decent odds that the other end isn't connected to anything either. Very slowly and gently pull the wire out of the wall and see if the entire thing comes out. Stop if you feel resistance. The use of a blank cover instead of an actual wall jack makes me think this is not a professional installation, so I'd wager the wires are just dangling inside the wall cavity and aren't anchored anywhere.
If you have easy access to the attic space just above this room, it may be easier to trace the wire and remove it from up there.
Should you decide that you want to leave the wires in place just in case someone wants to use the speakers in the future, you can replace the blank wall plate with a speaker wall jack. That looks much more "intentional" than a big blank cover plate, and you for two wires you can shrink the opening down to a single gang. A wall jack like that also clearly says "this is for speakers", so future residents won't have the same confusion you're currently experiencing.