I have some images in my home page and from time to time the URL of these images get changed somehow and a subdomain is appended to it automatically.
Here are some other facts that might have something to do with this issue:
The site supports two languages (english and arabic which is the default language) and this issue only appears in English Site.
We had a very old drupal 6 site before that was using Subdomains extensively (using the subdomain module) and I noticed that any subdomain appended to the image url is usually a randomly selected one of these old subdomains. So these domains used to exist. But the weirdest thing is that we actually moved to a completely new server a year ago and we created this new site from scratch using Drupal 7. We have not imported any content or modules from the old site and we don't use subdomains any longer. The old server is no longer active. Also we have removed all subdomains from DNS in cPanel.
The issue goes away sometimes after clearing the cache.
What could be causing this weird issue?