Chrome has some nice dev tools which allow you to see each individual request on a page. If you can reproduce the problem in that browser then the tools may give you some useful information such as a http status code. Also check your server error logs.
My background loads then turns white for users pretty frequently on many different pages. First we thought it was because we were not hosting the image ourselves, but I started hosting it and it is still happening. I haven't gotten any real answers in the other forum sections so I think it may be a bug of some sort. Thanks. Running 1.1 RC1