Your LFM-1 most likely bottomed out. You probably calibrated your subwoofer lever too "hot". Since you have your SPL meter, try that scene again after proper calibration to reference level. You have to have a happy medium between receiver volume level set and subwoofer's gain level. Also placement of subwoofer location play big with how loud your subwoofer able to play before it bottom out. If you still have pop even after proper calibration and optimal location, you might need little more subwoofer power for your listening level. Good luck. And welcome to Outlaw family.