Yet another vibe question

Alright folks, I used the search tool and was not able to find an answer to my problem. I recently installed the 5100's up front on an 02 4x4 x-cab. I waited aboot a week after to get the alignment. Well, after the alignment I noticed a kind of throbbing vibration. it feels like it's in the driver side somewhere. It ONLY does it when its really cold in the morning then seems to go away after driving about 10 miles. I live in SoTex and we hit a warm spell recently and on warm mornings, no vibe!? The funny thing is the fact that there was no noise before the alignment. Oh, The vibe comes only between 32-40mph. Do I just need to get another alignment or am I looking at the differential bearing? HALP!