It’s common for a guitar amp to produce hum/noise under high-gain settings, like the default Channel 4 (Metal) preset on the Spark amp. Such noise can usually be tamed by positioning the guitar in a different direction, touching the strings, knobs or the bridge on your guitar, or adjusting the settings of the Noise Gate on the signal chain in your Spark app, depending on the gear and the settings used on the amp and/or effects.
Please refer to this video, starting from 19:17, and this video starting from 2:23.
The default Noise Gate settings in most Spark presets are subtle and neutral to help preserve your guitar’s natural sustain as much as possible. To achieve the ideal noise level, try adjusting the settings via the Spark app according to your gear, setup, and environment.