Buckling of vinyl siding can be caused by a few factors. Vinyl expands and contracts and if it is fastened too tightly to the wall, this expansion and contraction can cause buckling. Also if the joints between siding panels are not treated correctly, the expansion and contraction can also cause buckling. The last thing to consider is a possible product defect. Contact a qualified siding installer to take a look at the installation, it may be a very simple fix.