keep an eye out in the bike shops for a little gadget that you can insert into your exhaust to quieten it down a bit...... it's just a tip that you can screw into the end of the can (you have to drill a tiny hole on the under side of the tip - not visible) that does a damn good job of queitening things down.....and it's removeable for when you don't mind being noticed!
You can also find them on the uk ebay site
www.ebay.co.uk