I get the feeling a lot with plantings. Flowers and really colorful bushes or trees especially. I think the colors play a huge factor, they bring in entirely new textures and change the scale of the landscape completely.
Certain grasslines and mowing patterns clutter the picture for me as well. I find having excessive amounts of cut heights, or overly regulated and stark transitions to be distracting. If you add in a lot of stripes, I can certainly be overwhelmed with all excess lines and edges. This is absolutely visual clutter to me, as it is distracting from the composition.
Honestly, excessive bunkering can cause visual clutter for me as well. Whether it is an egregious amount that over dominant the landscape in the wrong way, or far to much sand that it is dominating the scale, or just way too many wiggly lines that distract from the bigger picture.