Did you try the grommets with the shroud? Or, maybe small pieces of duct tape on the corners? The shroud is there to guide the air for more efficient airflow -- are you using the fan to pull air up through the HS or blow down through it?
I knew it was supposed to guide the air, but it hasn't affected temperatures one bit. Maybe the intake cover is just one of those things that was better in theory than practice.
Once I determined that, there wasn't much reason to figure out a way to silence it and put it back on.
Doing all kinds of things today (off sick).
Just pulled the fan off my videocard and running it with a little Alpha heatsink, and a 80mm L1A at 8V blowing on it from a Zalman side bracket.
Not as succesful - video card tems are up 6 degrees C, but the card is still stable.