Cars are expensive to run, and unexpected suspension noises always pop up at the worst time. That loud humming noise that gets louder as you speed up usually means a shot wheel bearing. Repair shops tend to be slower in late winter and mid-summer, which is when you might get a slightly better break on labor rates.
You should always negotiate labor or bring your own parts before you talk about how you are paying. For a $400 job, breaking the bill into manageable pieces keeps your cash liquid while you get your car back on the road safely right away.
A 0% APR window is not free money—it is just a temporary shield against interest. If you still have a balance on your card when those 18 months end, the regular APR kicks in on whatever is left, so stick to the $22.22 monthly plan.