I have one phone line that has an awful hum. The others, connected to the same hub, are fine. It's the line not the phone, I checked. I've replaced the inside wire but the hum is still there. Is there special IW or a filter that can be installed to eliminate the noice? Thanks.

One of your wires likely touching a ground.
Unplug anything pluged in to phone jacks, also, do you have innercomm, door system, gate entry, Alarm system, anything that uses phone.
A lot of the newer phone boxes(outside), allow a test point.
Take a known good phone and plug in(have to unplug jumper first(same as phone cord)
Try another known good phone and cord, in case first was bad.
If you still have hum, Telephone company will fix for free, if after that box, then you pay.
Do you have more than one line?

I have found that the newer phones that use a power supply that plugs into the wall, can be causing this problem. Try unplugging these types of phones one at a time and see if the problem goes away. If it goes away, toss that phone and don't buy that brand again!

Two things come to mind. Bugs/spiders or anything that can bridge a telephone connection.
Running a line in parallel to an electrical line can do it too. Polarity can be reversed. Some phones care and others do not, so check the polarity or try reversing the connections (Tip and Ring).

Also, if the phone is plugged into a surge protector, try going straight into the phone jack with it instead.