There's more than just noise you need to address when practicing plugged versus unplugged. *If you are plugged in, your dynamics are much more evident. *More importantly though, you will find that the way you fret the note really shows, especially with your distorted tone. *Sometimes I can practice unplugged and think I am playing pretty good, but when I plug in using the same technique, it sounds bad through the amplifier. *I also think it is important to practice at the volume you would usually play at, as your amplifier will be a different animal in many aspects, not just noise.