If it IS exhaust, you should be able to crawl under the car and find
something loose.

Does the ticking increase with speed?  Do you hear it cornering hard?  It
maybe wheel bearings, they will make a ticking sound and a easy to replace.
Jack it up and see if there is any play in the rear wheels, grab top and
bottom and wiggle, both sides and wiggle.
If your state does safety inspections, they may actually remove a wheel to
inspect and they may not retighten to the correct torque specs.  Happened to
me, they inspected my car and two months later I had to replace rear wheel
bearing......