The crackling sound is most likely to be a problem with your switch. If it only happens in the one position then try blowing it out, and if that doesn't work then buy a new one, they aren't expensive.
If the sound from your amp is a humming, and it stops when you touch the strings, then that's normal, unless it's too loud. Plug your guitar in and touch all the metal pieces, if the humming dies at each touch, then the guitar's grounded fine.
The humming isn't feedback, it's static electricity.
