To reduce pollution
Removing the EGR increases pollution.
The EGR is designed to recirculate exhaust gases in order to reduce NOx levels and meet emissions regulations. In doing so this it hinders performance. People remove this system in order to gain the power lost.
It will likely be the VVT-i assembly located in the end of the intake camshafts. We had it rather bad, so I moved to a thicker grade oil(still within specs) and haven't had any issues or rattles since. Does it go away a few seconds after starting?
Note that only the 3-rib/bluetop bigport 4AGEs have the screw-in air temp sensor in the intake plenum. 7-rib bigports and smallports have them as a plug-in sensor in the airboxThis is true.
You will be paying in the $80-$90 range for an OEM one as well.