Plugging the silencer ports is usually a bad idea.
A few people have used QuiKSteel and haven't had a problem. But me on the other hand, used QuikSteel and after 3,000 miles, one of the QuikSteel globs I used to cover to silencer port couldn't within stand the heat and dropped in my engine. Not a good thing.
Turned out Alright as I rebuilt everything the block up and included all the mods in my Sig.
There is also a write up on here how to do it the "correct way"
Point being though, do it at your own risk. Some have luck. Others don't. For me, after learning the hard way, the extra whine wasn't worth hurting my engine again, if something went wrong.