Thank you foryour answer mattbennett1, But, all of my respect, I have to say, no. The switching on/off noise will be there anyway. Just you haven't noticed it yet. This is a standard problem caused by inductive loads: Transformer core is magnetically natural and in the first start, it acts nearly as an ohmic load. When you switch it on slowly or you switch it on during sine-wave peak, you can easily generate a huge peak. For the same reason, many devices having specific noise filters and switch-on/off filters. Most probably, you haven't connected your sub in the same way and / or not closely checked when switching it on and off. This switch on noise is not big, just noticeable. But, when I switch on my Eris speakers on my desktop prior I'm switching on the sub, I have this small "pop" noise. The fact is that this unit has no noise-filter on it's power inlet line which could help to avoid these like transient caused problems. It is not a big deal to implement it in the future releases. I'm planning to add it to my sub after I already tested the issue just as I'm added the required filters so many amplifiers I built.
After I written this down all, I realized that you probably speaking about your Eris E8XT instead of Eris Sub8, which causing the problem. E8 XT having a different amplifier inside therefore it will be totally different from the E3.5 and Sub 8.