DD LFE vs DTS LFE sound tracks on the same disc, the DTS track will be 10dBs higher than the DD track. DTS records their tracks this way vs. DD. Not sure if this could be the cause of your problem but I recently purchased the 990 and noticed it compensated for this difference. My old Parasound AVC-1800 surround processor didn't do this and I always had to manually lower the subwoofer setting by 10dBs to compensate for the difference.