New to the forum and a newbie with amplifiers (older acoustic guitar player).  Noise (hum) from amplifier after powered up.  My son (14) acquired a Line 6 Spider III 30 (SN 21A851P5749xxxxxx) and a Harmony Guitar.  I R&R'd the plug, potentiometers, switch, capacitor, and wiring in guitar (I have some electronics experience and original hardware was junk - replace with switchcraft and WD) and set up guitar to factory specs.  When we turn on the amplifier with the guitar plugged in:

-noise (hum) until I move channel volume switch (up or down) or hold Tap delay and rotate past 12 o'clock

-noise (hum) when switch from "clean" to other setting (crunch, metal, insane) until I move the channel volume switch (up or down)

Note, I do note a small bump when I turn on the amp and a significant bump when I turn off followed by a second bump after the "switch off" bump.

Don't know what is normal and don't have  a wiring diagram for the amp to troubleshoot the noise (hum) easily.  Any help would be appreciated.