Engine knocking

I have a 98 Cherokee and today it was bit rainy out and chilly(go figure live in ohio) So the Empty light just came on went to Dshell gas station got the 87 octane as normal which i have been doing for years... then i merge back on tap the gas a little bit then this noise starts. It does it only when i hit the gas pedal or if it is in idle, the higher the rpms the louder and faster the clanking. Does it sound maybe like a bad batch of gas or should I consider taking it to a mechanic?