rattle in 105

There's an annoying rattle coming from the housing of my brand new front/left Shimano 105. Sounds like a loose screw or spring. It's only heard when riding on a slightly rough road, but it's quite audible to me. I can reproduce it by dropping the front of the bike an inch or two off the ground. It doesn't happen on the right/rear shifter. It's definitely not the face cap. I tried tightening all visible screws and regreased. The dealer acknowleged the rattle, couldn't fix it, and replaced the shifter with a new one (under warranty). The new one makes the same noise!!!!! I called Shimano. They said rattles weren't unusual, even in new shifters. The rep thought it may be due to the cams, which are inaccessable. Anyone else have this problem? Anyone fix it? Am I only one with a loose screw?!?!?