If the wire is popping or stops and starts, the wire speed is set too fast or slow. If you are feeling "kickback,” the wire speed is set too fast. The wire speed must be fine-tuned with slight adjustments.
If the wire is popping and won't stick, you may have the wrong wire, the surface you are welding may not be clean, or you may have the wrong gas if you are welding MIG. For mild steel, you should use 75% argon and 25% CO2; for aluminum, use 100% argon.
Make sure you are using a dedicated 20-amp circuit with no extension cord.