Interference issues with monitors and audio systems when using a laptop as a desktop setup are often caused by electromagnetic interference (EMI) from power supply cables. To mitigate this, it's crucial to avoid running power supply wires parallel to audio or monitor cables, as proximity can exacerbate interference. Using ferrite toroids on speaker wires can help reduce this interference; the wire should be looped around the toroid for maximum effect. Additionally, wrapping monitor cables with EMI shielding tape can further reduce interference, especially if the monitor output is located close to the power plug. If problems persist, considering an EMI filter may also be beneficial. The type of power supply, such as a Switch Mode Power Supply, can contribute to these issues by allowing some AC noise to slip through.