Whistle after cabin filter change?

[blue-sun]

So I changed my cabin filter on my MS3 finally this past weekend. The old filter was nasty!

This morning on the way to work I noticed that the HVAC system has a high pitched whistle/whine to it now.

During the re-install I was missing the top screw of the cabin filter cover. I found the screw later, is that why it's whistling? Did I not put the filters in correctly?

Any ideas before I pull everything out again.

 

[WillD]

Maybe the filters aren't locked together and the air is whistling as it passes between them?

 

[blue-sun]

Yeah, I figure once it gets warmer here I'll take it all apart again and make sure everything is in there correctly.