Please perform a factory reset to roll the unit back to its factory settings to avoid any unexpected errors. By doing so, all existing presets on the BIAS Head/Rack will be replaced with default presets. Please make sure to backup your presets first. You can log into ToneCloud and use the Back Up & Restore feature in the settings menu to save all your presets from the unit to your ToneCloud account. Also, please update the BIAS Head/Rack to latest firmware version (0.5.1.231) and see if the noise dissipates.
If the noise issue persists, please open a support ticket at: https://help.positivegrid.com/hc/en-us/requests/new