How can you spot a flawed bandsaw blade?

When I make a cut with my bandsaw, the blade drifts forward and backward. At any given moment, the teeth might or might not be in contact with the workpiece. The wheels are co-planar with new tires, so what can I do to fix this problem?
—Greg Marble, Oakfield, New York

Look to the blade for the problem, Greg. Either a poor welding job distorted the blade, it was bent during use, or the steel warped during manufacturing. In the first case, an expert might be able to fix the problem by cutting and rewelding the blade. If that doesn't help, your best bet is to buy a good-quality replacement.