"The octane rating is a measure of the resistance of gasoline and other fuels to detonation (engine knocking) in spark-ignition internal combustion engines. High-performance engines typically have higher compression ratios and are therefore more prone to detonation, so they require higher octane fuel. A lower-performance engine will not generally perform better with high-octane fuel, since the compression ratio is fixed by the engine design." "Many high-performance engines are designed to operate with a high maximum compression and thus demand high-octane premium gasoline. A common misconception is that power output or fuel mileage can be improved by burning higher octane fuel than a particular engine was designed for. This is not true. The power output of an engine depends in part on the energy density of its fuel, but similar fuels with different octane ratings have similar density. Since switching to a higher octane fuel does not add any more hydrocarbon content or oxygen, the engine cannot produce more power." "Most fuel stations have two storage tanks (even those offering 3 or 4 octane levels), and you are given a mixture of the higher and lower octane fuel. Purchasing premium simply means more fuel from the higher octane tank. The detergents in the fuel are the same, Premium does not "burn cleaner."" Wikipedia You need an engine with a higher compression ratio to burn all of the higher octane gas. The ECU has little to do with it. You can always rebuild an engine to a higher compression ratio but there is no need to use high octane gas in a regular untuned engine. I need high octane because my engine has a 10.5:1 compression ratio... The sound could really be anything though. Do a thorough seafoam cleaning through the brake booster line and crank case. Don't forget to change your oil right after you do this.