The antenna is not the proper length. 
Extend the antenna fully; replace it if it is broken.
 
The antenna is poorly grounded. 
Make sure the antenna is grounded properly at its mounting location.
 
The station signal is weak and noisy.
 If above solution does not work, tune in another station.

You are in a weak signal area. 
Make sure the tuner is in DX mode. 

If the area you are in is a primary signal area, 
the antenna may not be grounded and connected properly. 
Check your antenna connections; 
make sure the antenna is properly grounded at its mounting location. 

The antenna may not be the proper length.
 Make sure the antenna is fully extended; 
if broken, replace the antenna with a new one.

No antenna, or open connection in the antenna cable. 
Make sure the antenna is properly connected; 
replace the antenna or cable if necessary.