Scratchy pops coming from the left channel when I turn up the volume why?

Plug in another source component to verify it's the preamp.

It's not shaft you spray (will be the same thing as if you spray kitchen sink) you have to spray POT. To get to it you should remove either top or bottom depending where the pot is mounted. Need to direct the straw DIRECTLY onto the pot and rotate it in/out few...several dozen times while spraying.
Than you need to let it dry for few hours before you turn preamp back on.

Sounds like the name of a new breakfast cereal.

Jiggle the power supply. Make sure it is plugged in to the input on the back.  Secure it.