Poor TV reception in Manchester?

Any ideas - last week the bundle of Channel 4 (E4, C4, More4, C4+1) channels started to go down on my freeview box and also on my DVB TV. The ogue reception has become almost unwatchable too. The confusing thing is that the other bundles (BBC, ITV, other freeview) are working nearly perfectly. Is there a problem with Winter Hill? Who should I report this to?