Moonroof wind noise

This doesn't seem to qualify as an appearance or performance mod, so I hope this is the right place to post for help. My 08 CTS has an aftermarket moonroof that the prior owner had installed. It's a nice feature and all, but the wind noise at 45+mph is just not acceptable. It sounds like having a window that is slightly-open ('cracked') all the time. The roof has no leaks, and the seal seems to be in great condition. The glass seems thick enough, but I'm no expert in that regard. I've dealt with it until now, but I'm looking to finally fix the only thing that bothers me about my great car. Any ideas on how to quiet this noise down? Thanks!