I have made endless cakes but I am still getting the same problem with sides that are bulging/rippling.  I have tried and taken so much advice about resting my cakes, buttercream dams, torting and double crumb coating.  This week I made a madeira thinking it would be a lot more solid to work with and less chance of rippled sides - I even marzipanned it - this morning the marzipanned cake looked straight and lovely and smooth.  But as soon as my fondant went on it looks awful.  I use smoothers etc.  Where am I going wrong?!  Why can't I master this?? I'm going to give up at this rate. ;-(  

AHave you tried applying the fondant to a cold cake?

AAnd keep it cold afterwards to set the fondant and keep it from stretching? it's invisible glue

yes K8 - I usually chill my crubcoat and fondant cover a short while after taking it out of the fridge.  Although this time as i had marzipanned the cake was room temp.

Aare both sides of each layer level?

yes - I'm careful to tort each layer and I use a spirit level to check they are level.  I usually cook one size bigger as well and I trim  (using the exact size cake drum) to size so that each layer doesn't have any brown crust at all. 

what kind and how much icing is on the cake before fondanting -- was there anything under the marzipan? double crumb coat? how thick is it?

I am wondering if you are 'settling' the cake in the fridge so that whatever you are filling with is actually setting firm and then letting it sit out at room temperature so that your filling is softening and therefore bulging under the weight of the cake as it comes to room temperature. You could try settling cake at whatever temperature you will be serving it at to ensure that the temperature change doesn't affect it.

The type of cake has very little to do with the filling bulging out except for of course a heavier cake will put more stress on the filling, Your filling really needs to be able to support itself as the cake will not hold your filling in. Perhaps you could try a thinner layer if filling?

Since I have turned to doing ganache under the fondant I do not have any more bulging or melting issues with my fondant.  Ganache creates a hard shell that hold very well under Fondant.

A

I use ganache also and it has completely changed my fondant cakes. I also think very thin fondant (rolled to 1/16" thick) is easier to get smooth.