My 1997 Jeep Grand Cherokee has a rumbling, slightly metallic noise coming from the rear of the vehicle. (I do not believe this to be tire noise since I rotated the tires and no change). This noise starts at about 25 MPH and is more pronounced when the vehicle is under load. When you take your foot off the gas the noise greatly reduced. I have replaced the wheel bearings which did not help. The visible gears show no wear and there was no significant metal filings, etc in the differential case. Where next?

Just got back from the dollar store. They had a national brand of the stuff. 12 oz. bottle. Treats up to 20 gallons. Besides other various claims made on the bottle it says it improves gas mileage. Obviously then comes the question: Is it worth the dollar? And what do you suppose the "petroleum distillates" is, that it is made out of?, that they can sell the stuff for this price. Maybe if we knew what it was, we could make our own even CHEAPER. The manufacturer must be making a profit selling it for the dollar, even after shipping costs and the retail stores cut. (It sells for higher at other stores.) And just how much does it raise the octane level in a tank of gas, since they call it "super"? What if you dumped the whole bottle in 10 gallons as opposed to the 20 gallons? If your car does not ping now, is this really going to help the car's gas mileage? Doesn't high octane actually slow the burn? You would think you WOULDN'T want that. You'd think if the gas burned slower, in theory, that it would still maybe be exploding as the exhaust valve started opening. You'd think you'd want the most rapid fire of gas as possible without the ping. What can you share about this?