I bought a HJC full face helmet when I bought my Buell Lightning in '04.
Not a spectacular helmet , but it did the job pretty well and was fairly quiet.
2006 comes along and the Buell gets totalled , long story , then I get a '06 FLHT.
The FLHT seems a bit loud , so I buy a HJC half helmet so as to look like a Harley rider.
The half helmet is much more quiet , more wind noise , less everything else.
I can hear traffic better and the bike is more muted.
Then I grab a pair of Vance and Hines classic mufflers , and do a stage 1 job.
Bike sounds pretty neat now , so I try my full face helmet for a short ride.
Holy Crap!!! is this bike loud.......
Needless to say , the full face helmet amplifies all engine/pipe/mechanical noise really bad.
I guess I really like the half helmet combo , the noise type and sound level of this helmet makes me more comfortable and I enjoy the ride more with it.
I would try and run your bike for a bit without the windshield and see if this is a comfort level you can live with , as we all know , the full face is safer in a crash anyway.
This was a repeatable sound thing for me also , the full face always sounded pretty bad , even with a short windshield for me.
Good luck.
Mick