I have 2010 Subaru Impreza, there has pinging/knocking noise and quit noisy when getting up hill. Is there a way to fix the problem?

Check your oil level. Also it could be the timming is slightly off cause the motor to detonate too soon.

Thanks Michael. Actually I just got the service done 2 weeks ago, I told the technician about the noise and the technician told me to fuel in chevron primium gas Instead of regular and see if the noise will gone. Will it make a big different?

pinging/knocking noises come from pistons trying to compress a mixture on fire too soon or advanced timing, using premium gas has a higher octane rating which burns slightly slower resulting in an effective "not as advanced timing", or later, or retarded timing, resulting in less or no ping or knock. Compressing an explosion is what results in knock.

Oh and will it make a big difference? driving style will make more of a difference than higher octane gas, a lead foot will cause more knock than anything so easing up on the throttle will also reduce ping/knock.