The best way to mute unintentional string noise is to learn what's called "Thumb Muting"

It will take a few weeks of consistent practice to really get down, but if you play on a regular basis (which it doesn't seem like you do), it will be totally worth it.

Let's just say that when you NEVER play with excess string noise, it will make you sound TOTALLY PRO (like Joe Satriani). Perhaps that will be enough incentive for you to a) start playing more and b) practice thumb muting!

Now, I could explain how to do this... OR I could link you to some very valuable resources that will explain it for me. I think I'll do the latter.

Here are 3 articles you should read.

1. How to Improve Your Guitar Technique and Play Clean Part 1
http://tomhess.net/ImproveGuitarTechnique.aspx

2. How to Improve Your Guitar Technique and Play Clean Part 2 (Stop Unwanted Guitar String Noise and Sloppy Guitar Playing)
http://tomhess.net/UnwantedGuitarStringNoise.aspx

3. Picking Hand Discipline
http://tomhess.net/Articles/PickingHandDiscipline.aspx