HTC Sensation Navigation screen flickers

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http://androidforums.com – Hope I am in the correct forum. When I start up the Google Maps Navigation app that comes as 'default' with the HTC Sensation it lets me go to the screen where I can type in or speak the destination but if I type in the destination or press on one that I have used before the Google Maps Navigation 'splash' screen appears for about a second and disappears. When I do get it to work the screen flickers between the maps and the phone's 'desktop' screen. The automated voice I have downloaded and used many times is still audible despite this. Any ideas? I don't know if it is linked but also now whe (General)