Thanks for your posting. I am not using their Bass Alignment Unit if that's what you mean.
The oddest part for me was the level would fluctuate over time. Sometimes, once it reaches the normal level, it would stay at that level. I don't have any actual data, but my impression is that if I play that channel at high/reference volume for a while (i.e., when I calibrate), it tends to get better. As a surround channel, the speaker normally would not get that much work, but it feel as if, it needs to "warm-up" by playing at higher volume before it stabilizes.
I have indeed switched the channel output from the amp end and the same speaker remained problematic. I guess I have not officially ruled out the speaker cable but that really seems unlike.
I forgot to mention the reason I haven't taken the speaker apart and looked inside is because they were mounted high up on the wall and not easily accessible. So I am hoping to have some idea what might be wrong before I proceed further.