Hello -- If you had referred to only a single dip, I might have suspected that this could be as simple as a center support issue, which can often be solved just by getting a bed frame that has proper support going up the center of the mattress (not just on the edges).

However, since you refer to "dips" in the plural, it sounds like you may be experiencing something that's known in the mattress industry as "body impressions." Since the advent of "no-flip" mattresses with lots of cushioning, these have become a fairly common phenomenon. Some people actually like the feeling of nestling into a familiar spot in the mattress, but many (like you) aren't fond of them. They are caused by settling and compression in the foam cushioning layers at the top of the mattress.

In terms of what can be done to remove them, the easiest answer is to try to "even it out" by sleeping on the parts that are still poofy. Of course, this will mean sleeping in the parts of the bed where you wouldn't ordinarily intend to sleep (eg, the middle and the edges), so it may not be practical to do.

Another option is to try flipping over the mattress and sleeping on the bottom side of it. Note that this is technically not how the product was meant to be used so you'll have to read the fine print of the warranty to make sure this doesn't violate your warranty. Also note that since the bottom is not intended as a sleep surface, it almost surely won't be comfortable to you unless you buy some kind of "mattress topper" to put on it. In effect, you'd be turning your one-sided mattress into a two-sided mattress in order to even out the body impressions.

Lastly, if the dips in your mattress are deeper than 1.5" (when you're not on it), then this may actually be considered a manufacturing defect, in which case it would be covered under your warranty.