I'm new to the 4 strokes.i bought a kx250f at an decent price but bike has an unusual noise coming from the engine?

 

Can you describe the noise for us? What year bike? Where do you live? whats your credit card number and SS# LOL just messing, welcome to the forums. It could be the cam chain tensioner, might need adjusted or replaced. That will sound like a slight to loud ticking up high on the motor.