You really have to clean your filter sponges very well by squeezing them in buckets of tank water. Continue to do this until your water is completely clear. You may need to also rinse your other media better as well in tank water. Don't worry about killing your BB by rinsing in tank water. A highly clogged sponge will build pressure which is causing your media basket to raise. When I first got my AC 70's they did the same thing. Only after repeated cleanings of the sponges did they finally come back to where they should have been which meant my media hasn't ever been pushed up since. I clean each AC once a month by the method above and I haven't had this pressure buildup in two years. Here's an excerpt from the AquaClear manual below:
Q. What happens if I forget to clean my filter inserts?
A. If the Power Filter is left unattended for too long, the filter inserts
become clogged with debris. In extreme cases, the filter basket may
be forced up from the filter case due to the pump pressure. This is
an indication that the efficiency of the filtration is very low and
that the filter inserts require immediate rinsing or replacement.