Lumpy, uneven horizontal surfaces

[dcroxton]

I'm a few weeks into 3d printing with a Creality 3 pro. I think I have the bed levelled and my prints are turning out well for the most part. For some reason, however, prints with large horizontal surfaces often come out lumpy and uneven, such as the one on the right below. There is obviously some kind of buildup happening; I can hear the print head dragging over the raised areas. I haven't been able to find out too much about this problem online.

I assumed the problem was from over-extrusion, so I cut back the flow to 90%, infill to 15 (from 20), and also tried dialing back the temperature to 195. This worked for the most part (left image) but I'm not sure if it's the best solution. The one on the left looks like it didn't get completely covered on top. I'm also still getting some really uneven sides. The first layer looks beautiful, but later bits stick out, which I thought would have been solved by lowering the temperature and flow rate. Just wondering if this is a common problem and if anyone has suggestions.

IMG_20200506_192932291.jpg