The engine knocking sound: sounds similar to a diesel engine. I have a similar sound that comes and goes at startup. Had a dealer, indy and mod-shop all diagnose and they said there's nothing wrong. May be common with the "IS" models.

Exhaust: it pops and burbles a bit. This is common on startup but if it continues, the previous owner may have replaced the resonator with an x-pipe or straight pipes. Do a search for exhausts and compare to your setup, there a plenty of pics of different setups.