most typically this is from using too low an octane of gas resulting in incomplete detonation or "pinging" try gas at a different station or move up a grade of gas. Other causes could be poorly adjusted lifters, exhaust leaks etc.
I think most likely it is the gas, at least sounds that way. I am using Mobil or SUnoco 87 octane. Since I drive about 200 miles a day moving up to 89 octane is not a good solution, however I will give it a try for a week (that will be 5 tankfulls )
You could also go to autozone ( or some shop like that ) and check your codes.....maybe you have a pending code (meaning it's not quite bad enuf to throw a CEL ) on a O2 or temp sensor...hey.....that's cheaper than gas! And since I drive 130 miles everyday.....I feel your pain!
that definitely sounds like detonation. if that is the case, i would first try a "good" brand of gasoline, like chevron 87 octane. if the problem continues, move up to 89 octane. if that solves the problem, stick with that. you'll save more money in the long run by preventing damage to your engine.