Find the sound config file here:

C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X\Captain_Sim\757

open the sound config file and find SoundOffWhenSimIsSlew=1 and change the 1 to 0

For free liveries, including American Airlines, go to support and check in, and click on your product.  You will find a number of links, including Get Free Liveries.  Browse to your heart's content.

Most issues have been covered by previous posts, so you can probably find what you need right away through the search function.