There is no traditional noise source on the Phatty series, but there is a workaround involving the mod source. In the Master Menu, scroll over until you see Advanced Preset, and hit Enter to access this menu. In the Advanced Preset menu, scroll until you see Mod Source 5 or Mod Source 6.
MOD SOURCE 5 (MOD SRC 5):
This menu allows you to select one of two modulation options that will be used when the FILT ENV source is selected on the front panel (Modulation Source 5). FILT (Filter Envelope) is the default source, but S-H (Sample & Hold) can be chosen as an alternate. To change the parameter, use the CURSOR button to highlight the parameter, then use the VALUE knob to set the new parameter value.
MOD SOURCE 6 (MOD SRC 6):
This menu allows you to select one of two modulation options that will be used when the OSC2 source is selected on the front panel (Modulation Source 6). OSC2 (Oscillator 2) is the default source, but Noise can be chosen as an alternate. To change the parameter, use the CURSOR button to highlight the parameter, then use the VALUE knob to set the new parameter value.
P.35 of Slim Phatty manual