Cracking noise in extruder. It seems to be some kind of cavity in the heatbrake  

Cracking noise in extruder. It seems to be some kind of cavity in the heatbrake

I hear a cracking noise when I extrude my filament, and the printer doesn't print anything useful.

It seems to be caused by the heat break. I recently opened the extruder at the spring-loaded door and removed any debris from there, but there was nearly none, and it's still cracking.

But today, I checked if the problem is in the hot end and noticed a kind of cavity in it. So, I removed the Bowden tube from the hot end and put some material in it. When I push it inside, it feels a bit like filling something, because it doesn't spill out directly from the nozzle when I push it in. And when I push it out again, I have much of the old color on the tip of the new color, about 20mm or so.

I tried to unscrew the heat break and readjust because it seems the heat break is a bit high, and I can see a slightly bit of the thread of it, but I didn't have any success. Any ideas on what to do, or should I replace the heat break?