I Just bought a 2011 Street Glide last month, rode it 1000 miles and during the 1k service, had a set of Rinehart 4 inch slip-on's installed. I took the end caps off, to turn them over so that the Rinehart Racing is on the bottom. I was kind of shocked that there is no packing in them. // My question is: If I were to add packing between the baffles and the outer walls, would the db's increase?

 

No the packing would actually make it quieter if you want to make her louder you'll have to cut out the catalytic converter or put true duals on.