I have a Prusa i3 printer with mk8 extruder. I am using PETG with (200-240/75-85) degrees recommended temp on it's box. but when I do printing i hear some knocking sound that means there is a problem in extrusion. last time I did increase my temp up to 270 degrees!! maybe this sound solved! but it damaged my extruder's screw's inner Teflon and I forced to change it!

Now I have a new nozzle and extruder's screw, but again I can hear this sound during the printing! I thought maybe it's because of very close distance between the nozzle and the bed, but when I increase the distance, the filament starts to warping!

My nozzle is new and it can't be for clogging. so I decreased the print speed from it's default 60mm(in Cura software) to 50, but didn't solve this sound. Also when I use pronterface and do extrusion manually, it works nice with 200 degrees! but I can hear the sound in 190 degrees. But when I do printing I hear the sound even in 200 degrees! Is this mean I must increase the temperature for printing? how much?

By knocking sound I mean the sound you can hear when you have a clogged nozzle and the extruder's stepper motor can't push the filament into it and rotates with knocking sound!