- Ensure your Z seam is not set to "random".
- Dry your filament. This can be caused be moisture turning to steam and popping.
- Extrude in midair. Watch and listen. Depending just how wet your filament is, you may hear popping noises and see steam.
- Just because your filament was new/sealed, doesn't mean it's not wet. I've had plenty of filaments come soaking wet even though they were sealed.
- Try a new nozzle.