Creaking pedals on an mtb?

I have an old 2001 GT Aggressor 1.0, been riding it for a few years. A few days ago i started noticing a creaking noise in my pedals. Whenever i pedal relatively hard and get to about the 6 o'clock position, there's a creaking/ cracking sound that sounds like it's coming from the pedal area. It kinda feels like the pedal is jumping a few millimeters ahead whenever it makes the sound. Someone help me out?