theres nothing i could ever think of that would cause a tire to do that after you get new tires other then balancing or bad tires, keep in mind most tire places do do a good job, though there are times where the weight is 1mm or smaller off where it should be and really isnt detected until you hit higher speeds wather a good garage or not any one will pull the tires off and reinspect there work, tires can kill people much faster then a cheesey mechanic putting a bad engine part in, so they take there work very seriously, i take my 89 to a hole in the wall shop local to me ive gotten better service from them then any other tire shop and when i was concerned about bubbles i found on my wifes tires i had replaced less then a year ago they took a look and replaced the 2 i was concerned about with no other questions. take it back and have them rebalance and take the car for a freeway spin.