Swoosh noise on SMS

[Jimmy2shoes]

So I have had my iPhone 4 a couple of days now, not had any serious problems.
I restarted my phone last night and since it has cone back on, everytime I send an SMS I get a swoosh type sound that wasn't there before. I can only cure it by putting the phone on Silent, but then the text alert doesn't work.
Any ideas how to solve this and why it randomly started happening!??

 

[nospeed411]

I have had that since my first 3g model....they all do that it's never been an option to not have it