What type of magnolias are they? And what are the sun/shade and soil conditions in your front and back yard? Some magnolias are evergreen, and this could be a natural part of the tree defoliating. However, if you have a deciduous magnolia, something could be wrong. If you can post pictures it will help too.

I think it's natural defoliation. My neighbor's magnolia (evergreen) does it every year. Quite a few leaves turn yellow and fall off - it's doing it right now.

This is common for most broadleaf evergreens in spring -- hollies, gardenias, and magnolia grandiflora. They drop old leaves for new.

Broadleaf evergreens, such as magnolias, do not keep their leaves forever, they just always HAVE green leaves. I forget the exact timing for the cycle, but I think individual magnolia leaves last 2-3 years, and then die and are replaced with new leaves. This is normal for the tree.

Conifers do the same thing, but it's not usually as noticeable when some of the needles turn yellow and fall off.

My Magnolias, Savannah Hollies and Laurel have leaves that turn yellow and drop starting about the beginning of April til about Mid-May.

They are all planted in the same area right at the road and they look terrible during this time.

This past week there are tons of new leaves on all the plants and everything looks great again.

It is normal.

Yeah take a look at any/all of the Southern Mag's in your area. They should be doing the same thing. Mine are dropping their leaves right now as well. It'll stop once the summer gets kicking.