When you run 'top' It should show a bunch of header information as you typed but then also a bunch of processes under that and this should update every second or two.. There should be a column labeled "NI". On one of my servers it is between "PR" and "VIRT". Check that column for anything with other than a "0" value. Those are the "nice" processes. A positive value means lower priority whereas a negative value means higher priority. By default most processes are usually at the "0" priority.
See
https://en.wikipedia.org/wiki/Top_%28software%29