‘Noisy’ images in WordPress admin

Hi all.

I have a strange issue with one domain on my hosting plan, which does not affect any other domains (same server, etc).

In the WordPress admin I have a few noisy and broken images. The words on the right (Discussion, Password Protect, Post Slug) have grey noisy/grainy backgrounds when they should be blue.

I have also installed Phorum and have similar problems, with certain gifs intalled with a module appearing broken/ invisible/ skewed (despite re-uploading via Cpanel, in binary mode, and so on).

I have installed very similar WordPress set-ups on several domains running on the same hosting plan, with no problems at all.

I wonder if anyone could suggest what might be causing this?