Because carpeting is tufted at an angle, side seams will tend to show more than end seams (side of the roll vs. ends), but if the installer is good those seams should almost if not totally disappear within a week as the carpet "blooms" (it's been in a crushed state rolled tightly until put on your floor). You may notice the yarn blooming in a 6 to 8" wide band that centers on seams, too. The heat from the seaming iron causes it to lift earlier than the rest.
If one seam shows for a few feet, then disappears, and shows again a little farther away, it could be normal & become better with a little time. It could also mean that the installer isn't that great at doing seams. Berber carpeting is especially touchy to seam invisibly & the mating edges must be carefully "row cut" before seaming for them to mate up correctly & not show.
If you feel the seams may not be done as well as they should & the installation was done by the same company you purchased the carpeting from, or was subcontracted directly through them, call & ask that a representative come look at the job.
If you hired the installer directly, you'll have to take it directly to the installer.
Hopefully it's a temporary thing, not a bad seam job; fixing them can be very complicated & will need to be done by an installer who's a real pro.