Weird, weird problem – all pages showing rss feed

Hello,
I hope that someone can help with this odd fault. I’ve got the same thing happening on a number of sites running various versions of WP, the fault is that every single page & category with the exception of the home page (home.php) seems to display the rss feed of the site rather than the correct page – the URL look right, it’s just that the rss feed is displayed on each page.

The problem seems to be intermittent, sometimes the sites do it, sometimes they don’t, it does it in IE and firefox, and I’ve had people up and down the country checking and they see the same fault.

The only conclusion Ican come to since I haven’t been doing anything to the sites is that its somethign at the server, which of course the hosting company deny since they bizarrely claim to not be able to see the same problem.

I did load Supercache onto 1 site, but I can’t see that effecting all sites.
I wonder if it could be some odd server setting, or perhaps some kind of caching effect at their end, or perhaps someone else (its shared hosting) has uploaded something causing problems to their sites?

If anyone could advise I’d be greatly appreciative, even if its just to post here and agree that you see the same problem.

The sites effected include:

insurancegroups.org.uk
champagnes.org.uk
seoexperts.org.uk
intermindsevents.com
diamondnecklaces.org.uk
antiquesilver.org.uk

plus many more

Thanks..