The whistle is your TB sucking in more air! That's a good thing! Most SVT TB's do it including mine on my cougar (added it) and it was the first thing I noticed after upgrading, kind of cool when you get used to it.
The MAF diffuser is added to SVT's to smooth air flow and create less turbulence for the MAF, its not required and you definitly aren't hurting anything by leaving it out.
