My speaker is twitching, how do I proceed?

First check the audio source and the gain/level settings, a clean music signal is absolutely necessary to exclude the head unit/amplifier as the cause. Did metal filings occur during installation (drilling out rivets / drilling mounting holes in the door panel or similar)? Metal filings / magnetic foreign bodies can get into the air gap between the coil and magnet via the ventilation of the loudspeaker and cause interference noises, in this case the loudspeaker must be sent in for inspection.