Telephone line problems

[lim88]

I have two telephone lines coming into a building into two separate BT master points. From there the lines are ran over head to another building with two secondary points on each line.
In the first building there are no problems. But in the second building there is a fax machine that works perfect on either line and two basic unexpensive looking phones that are ok on one line, but when on the other line, the one they are meant to be on, there is non-stop interference.

I have check all the connections on both lines and have checked for any damage to the cables and everything is fine.
As the fax machine works fine on both lines is it just that these two phones are useless even though they work fine on the other line, or is there something that could be causing this?

Thanks

 

[camerabloke]

Is the one with interference on it enabled for broadband, if so, stick a filter on each telephone

 

[HMD]

Is the one with interference on it enabled for broadband, if so, stick a filter on each telephone

My thoughts 2,
If not Try new phone point on the line with interference and or try master there...

 

[lim88]

I don't think they use any internet connection there. But I will have to check whether that line is enabled for broadband or not, that could well be it.
I did try a new secondary point on that line but had no masters with me. I will try that if there is no broadband.
Thanks