I have a 2007 Toyota Yaris with a little over 30,000 miles on it. Over the past year or so I've noticed some slight pinging when getting up to speed on the highway or climbing hills, but since last week the engine began pinging more frequently and a little more noticeable than before (maybe a bad batch of fuel?). So at my last fill up, I decided to put mid-grade (octane rating 89) instead of regular (87). This made the knocking virtually disappear. I don't mind using mid-grade permanently, but will using a higher octane fuel than what's recommended for my engine cause problems further down the road? Thanks for any help.