When I kick on the ac there is a very noticeable change in how the car sounds. It feels like the whole car is making noise because of it. Not sure if that's just the way it goes with long tubes or if there is a issue that can be dealt with.
When you kick the A/C on, the ecu should compensate by bumping the idles speed 150RMP or so. Try manually bumping the idle with your accelerator pedal to the same RPM with the A/C off and see if it happens. Loading the engine like that (the way the A/C compressor does) will make the exhaust slightly louder though.
The change in the exhaust note doesn't just happen from the idle air controller the ECU will usually add timing to increase the idle speed as well as it's much more efficient in controlling idle speed. This alone will change the exhaust note