I've been using cheap gas from Costco or Superstore (grocery store in Canada) since I bought our CT a year ago. About a month ago I started having a "rotten egg" smell coming from my car on quite a regular basis for about a month straight. After googling the problem, cheap gas can give off a sulfur smell. I've switched to Shell V Power for my past 4 tanks of gas... and I haven't had the smell since. Maybe it'll come back... maybe this isn't the fix... but it seems to be doing the trick so far.