Amplifier skippings

I have an amplifier hooked up to a SurgeMaster hooked up to a normal electrical outlet. I've noticed that when I say turn on or off a light on the same circuit as the amplifier, it will skip about one second. Anything can trigger this skipping, even when my fridge goes in and out of cooling mode or turning on the electrical heater for the shower.

Anyone knows what's the explanation for this?