External speakers "pop" at random times while iMac IS IN sleep mode.

This has been an ongoing problem for a long time. When I put my 27" iMac into sleep mode it goes to sleep just fine, but later, at random times, the external speakers pops. I can even hear it when I'm in bed at night. I tried a lot of things, and read a lot of 'solutions' online, with no luck. (by-the-way, the popping does not happen when I envoke the sleep mode, or when I awaken the machine) Yesterday, I think I finally found the cause and a solution. I decided to take a look at 'Preferences' - 'energy saver' options. There aren't many, but one caught my eye, "Wake For Network Access". I disabled that option by unchecking it's box, and the popping no longer happens. I suppose there might be a downside to disabling that option, but until I run into a problem, it stays unchecked. I a guessing that, for some reason, the network is seeking to access the iMac at random times during the day and night, causing the popping noise. More informed minds will have to fill me in on why.