Headphones making faint click when sound signal starts/stops on iPhone SE

I bought myself a used iPhone SE and while I've overall been enjoying it, I have noticed one mild annoyance - when I have my in-ear headphones plugged in, I've noticed that sometimes, such as when I tap a search or URL bar (which opens the sound producing keyboard) or start a song or video, I hear a very faint clicking sound coming through my headphones, which I've worked out as being an indication that the phone cuts out the headphone sound signal altogether when nothing is playing. I also hear the same noise a few seconds after a sound has stopped playing through them. It goes away on search or URL bars if I disable the keyboard sound option in my settings. Anyway, I was wondering what's causing this and if I should worry about it (seems as though it is most likely software related).