Is this a new installation or relocation?
Make sure the RJ-11 line cord is connected the the LINE input.
If you has a volt meter handy then check the center two pins (RED and GREEN).
You should get about 30V DC.
The voltage can be higher or lower on the distance from the telephone company central office.
Check for the phone cable path. Make sure it is not sit on top of transformer(s) / lighting fixture(s)
or
On Network installation,the output of your digital to analog converter.
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Tip and ring line can be reversed.
Just swap the two conductors on the phone jack / wall jack and see does it make a difference.
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Check on these items first and let me know does it make different.