Freeview engineers identified a fault at the Wrekin transmitter after some people in Shropshire reported having bad signal on their digital TV sets for up to four weeks.
There were no faults reported with the transmitter on the BBC's signal checker website, but further investigation by Freeview has found an issue.
A spokeswoman for Freeview said: "Following continued investigations into the interference to TV signals in the Shropshire region, engineers have identified a fault at The Wrekin transmitter.
"Work is currently underway to fix this as soon as possible. Viewers may find that they continue to see issues whilst this work is ongoing, however if they have an internet connected Freeview Play TV or one that has the players available to view, they will still be able to watch live and on demand content from the likes of BBC iPlayer, ITV Hub or All 4.
"We will update viewers as soon as this work has been completed and many viewers should find that their service is back to normal. If viewers continue to experience interference following the engineering work, it is likely that mobile signals could be interfering with their signal and in this case at800 will be able to help."
Some may find their signal improves if they use an at800 filter with their TV. Filters are easy to fit and can be ordered for free by calling 0808 1313 800.