Ive been fighting that same problem for a couple brews now.....
What it sounds like to me is that you are decribing chill haze. The beer is crystal clear until you chill it, and then it becomes rather hazy.
I did a couple things, and havent narrowed it down which one was the culprit.
1. I started adding my whirflock at 5 minutes instead of 15
2. I started using better base malts...i.e, Maris Otter, Fawcett Pale instead of regular ol' 2-row
3. I cold conditioned my secondary for 5 days before kegging.
Now, my beer has been crystal recently, and Im not sure which little bit helped. Maybe all 3, maybe 1, maybe a combination........
Start troubleshooting is all I can say. But alot of my beers have had a SRM of 7 or less lately, so clarity has been a big deal for me.