The best new muffler tips on the market are from CMI; XTS Mufflers. I just put them on my 38 Powerquest with twin 500's and the dropped the dB by 4, and sounds much better with no internal flappers to rattle.

I was not referring to the noise aspect of the rubber tipped flappers. I have only heard metal ones at idle anyway.

The concern that I have is that very few people use two methods to prevent water intrusion.
mufflers and flappers fine
but a lot of people are just using the flappers that come with the tips which is what I used to do. When we started putting thru hull on or 17 foot model Merc required to use two sets of flappers to meet installation guidelines. I had never even heard of this before but I have had water run up exhaust on a couple of old performance boats i have had

here is a link to a similar item that we use. I have something similar on ebay but don't want to appear to biased

http://greatlakesskipper.com/custom-...ssembly-single

Just seems like it would be good to know how important something like this is. I know people have had hydra lock. I wonder how often this is the cause.