How can I fix my car radio so it can work 100% of the time?

My car radio works about 20% of the time. When it doesn't work, it shows that it
is on and getting electricity. It just gives me a white noise. If I hit a bump just
right or if I hit it, it will start working again. After some time I will lose signal. It
sounds like a wire is loose but I have no idea on how to go about fixing it.