Speaker Feedback - transition sound

Whenever I'm working at home, I enjoy using my iPod classic (yes, it's true), computer, and/or iPhone SE as playback devices to accompany whatever activity I may be doing at that moment. I noticed that every time I use the 1/8" stereo jack chord that is attached to the external speakers (4 total - 1 bass and 3 smaller speakers) to my playback device, there would be a hum/"record skipping" type noise that would emit from the speakers. This sound is short-lived and occurs very quickly before the 1/8" jack is completely inserted; however, it is a noticeable source of noise.