Street noise thru ventilation

[jonothon]

the studio I've been building is coming out great. One thing that's concerning me now is street noise entering thru the ventilation system, which is all networked in the rafters. I think we've done a good job with soundproofing, close all the doors, and street noise pretty much disappears. But when I sit in total silence for a while, i can occasionally just barely hear things like large trucks, and it seems I'm hearing it thru the vents, even tho everything is lined.

Wondering if I need something blown in on top of all this stuff, or if I'll need to create some sort of enclosure. I'll take some pix of the attic space and post them here, if that helps.