I am baffled. sometimes my fondant looks great and sometimes it has ripples in the sides where the filling is. Usually it ripples out - not in. I don't do this sort of cake on a regular enough basis to compare what I've done differently! I will say I do put a stiff buttercream dam around the bottom layer, fill with filling, then let it set before putting the top layer on so its not filling spilling out. After this I crumb coat, wrap and freeze. When I'm ready to fondant I bring them to room temp first.

Am I using too much buttercream under the fondant?... is there some other explanation?

Please help! I've always hidden it with fondant cut outs so you don't notice but someday I'll want to do a smooth cake with no attachments....

are you letting your cake settle long enough once the top layer is on? , the weight of the fondant could be pushing your cake down that tad extra to make the filling splurge out? i know alot of people place something heavy (but not so heavy it will crush the cake ) on top to help speed up this process

Let your cake settle after filling it, before crumb coating it. Make sure the cake recipe makes a dense, firm cake, so that the weight of the fondant doesn't push down on the cake as it sits in place. I refridgerate my cake for about an hour before applying the fondant for added firmness, than stick it back in the fridge afterwards to help keep it firm. Also, fondant rolled to no thinner than 1/4" works for me.

Let your cake settle over night with a tile or something heavy on top. The next day trim the sides of your cake with a sharp knife. HTH

What do you do with your cakes while they are settling? Wrapped at room temp or in the fridge?

Crumbcoated and left on the counter. (I don't crumbcoat the top). Then I set a plastic or cardboard round on top, and place the tile on top of that. The crumbcoat will seal the cake and it won't go bad or get dried out.

Wrapped at room temp unless filling needs to be refrigerated