I was wondering if there was a product like this. Also, here in Canada (and other countries too), tinting the windshield is illegal. What if the film is clear? Would it still be illegal?
I've never heard of an acoustic tint (could be out there..), but there is a windshield material manufacturer (Saflex) that makes an acoustic layer for use inside a windshield.
They market it as "Saflex Q Series", and one of their biggest clients is Ford (via Carlite), which puts it in several of their vehicles under the SoundScreen® trademark. This PDF from Carlite (OEM windshield manufacturer for Ford) shows the many Ford cars with the tech in 2013.
Another article describing the technology: http://glassmagazine.com/article/auto/acoustic-windshields-the-quiet-revolution
More recently, PVB suppliers have developed vinyls with improved acoustic-damping qualities. These new interlayers are particularly efficient in the 1,500 Hz to 5,000 Hz frequency range.
The decibel reduction typically is 2-3 dB overall. Although not large, it results in a quieter vehicle interior that allows people to converse without shouting.
Acoustic vinyl also enables vehicle designers to decrease the thickness of the windshield without negatively affecting noise levels. This is particularly important as automotive engineers try to shave weight off vehicles to make them more fuel efficient. Acoustic vinyl windshields meet all of the same federal safety specs as regular vinyl.
S-LEC is one worth looking into, cost is unknown to me, or how effective it is as treatment.
Locally in Hawaii we have a tint that can be put on the windshield. Its purely a UV film, as it has no help on "tinting" the light transmission any darker than factory. You could perhaps put a few layers on there.
Thats probably about the thickest anyone is going to allow anything to be put on the windshield. Not sure how much it would help any acoustics. Maybe a last option to have one more layer of any kind, protect that nice car dash, or more rigidity up front.