Lately I've noticed that as my cakes bake they are forming squigley/bubble shapes in the middle. When I take them out of the oven the top has these shapes, which usually get cut off when leveling; however I don't know why this is happening.

You mention leveling the cake; are they domed? If so, then domed and bubbles could be caused by several things:

1. outside is setting faster than center. Moist baking strips will help--they really do work.

2. cake structure is too strong, preventing a consistent release of leavening and instead forcing gasses to push through center.  A low protein flour should correct. If you're already using a low protein flour, slightly increase leavening to weaken the structure.

3. Leavening isn't distributed evenly.  I'm in the Shirley Corriher camp in that I sift 3x to ensure even distribution. 

Do you mean like a bubbly looking cake suurface? Did you put the cake into the oven as soon as the mixture was finished? If you leave it standing for a while because you made batter for 2 layers but you don't bake them immediately this can happen. Or maybe the oven wasn't hot enough when the cake went in?

As julia 1812 said you might have air bubbles in the batter.  Drop the pan on the table a couple of times to pop them.   Also you don't have to get a dome that needs to be cut off if you bake at 300 degrees (for 20 minutes for any size/shape using one cake recipe/batter) then turning it up to 325 for an equal amount of time.  For larger increase the time at each by 5 or 10 minutes.  Example a 16" round takes about 45 minutes per temp.)  This will give you a very nice moist cake w/o that wasteful hump.

Thanks everyone.  I'm not getting a dome.  I drop the pan many times so I don't think it's air bubbles.  As Julia1812 says, I do put the cake in the oven as soon as I finish mixing the batter so I'll try letting it sit out awhile.  Also, as Norcalhiker pointed out, the outside is getting done a bit faster than the middle.  

No, don't wait to put them in the over please! Make the batter, knock out air bubbles and put it into the oven straight away.  

It might be a temperature issue in your case...?

I agree, I think your oven temp is fluctuating.

Holes in your cake are called tunneling. The main cause of tunneling is over-mixing! Also, what size pans are you baking? Does it happen with all sizes? Then this may be the reason. Remember to lower your temp for the bigger size pans.

Thanks Minabakes.  I don't have holes inside the cake.