[shorod]

It does sound like you may have an exhaust leak. I'm just a lurker on this forum, but I'm not aware that cracked exhaust manifolds, manifold studs, or other exhaust leaks are common on the LS. Maybe one of the regulars will jump in with info on that.

Since it's cold now where you live, you may be able to spot an exhaust leak by looking around the exhaust outdoors and see if you can see an exhaust stream coming from somewhere other than out the tail pipes.

Could the ticking that you are hearing when the car is warmed up be your fuel injectors turning on and off? Are you positive that ticking is a new noise on not one you are listening for now due to the possible exhaust leak? If so, it is normal for fuel injectors to tick audibly (under the hood) as they open and close.

-Rod