Box showing up around a logo in preview and in Dropbox

So here's the problem I am having.  I'll write Dropbox about it, too.  I am doing some graphic design work for a client with InDesign.  I am using the company's logo on every page.  When I export the work into Acrobat and create a PDF, it looks fine.  However, when I upload it to Dropbox, there's a strange halo within the bounding box.  It happens whether I use a png or a gif.  Fine on my computer, screwy when I open it in Dropbox or preview it in Finder (I'm on a Mac).  I sent it to my client and asked if she was seeing it as well and she is.  Both when she looks at it on the Dropbox site and on email and when she downloads it from both, she still sees it. I need to get rid of this ASAP.  Any thoughts?