Light switch and amp

I have old Exposure XV Super. On one paticular listening session later at night 1100 pm the amp just seemed super sensitive. To the point I could here a small nosie when I turned the light switch on and off in the room through the speakers.

This is has only happen once since I got the amp a month ago. What causes this effect? In this same session the amp was creating a huge sound stage. It almost sounded if the sound was coming from the wall and ceiling behind the speakers.

I have yet to get this affect again. It was really nice and I have not been able to recreate it. Any thoughts?

Thank You