When we plug in a phone upstairs, our modem reboots, and broadband speed slows

[johnpoliner]

I hope I have posted this in the right place!
When we first went onto broadband, we used microfilters, and at some point I disconnected the ring wire on our upstairs phone extensions, and found that this improved our connection speeds.
Later I bought and installed a Modified BT ADSL Filter/Splitter Faceplate for the the BT Master Socket from Clarity.it. This also seemed to help our speeds, but I found that I had now to reconnect the ring wire, as the phones upstairs weren't ringing without it.
The downside is that, every time we plug a phone into an upstairs extension, the modem performs a full initialisation, and the ADSL speed is reduced. When we unplug the phone, the modem reboots again, and the speed is restored.
I understand that this is being caused by noise on the line. So far I can see our options are:
1) remove the Filter/Splitter Faceplate, disconnect the ringwire, and reinstate the microfilters
2) go over to a wireless phone.
I would rather not go down either of these lines. Does anyone have any other suggestions? It would be wonderful to be able to locate and deal with the source of the interference, or, failing that, to screen against it.
We are using a Belkin N Wireless Modem Router (f5d8633-4), plugged into the BT Master Socket.

[Rik]

Hi and welcome to the forum.

Something odd is going on, most modern phones don't need the ring wire. What else, if anything is connected to the line?

[Ray]

 

[johnpoliner]

We have three phones - one is also an answerphone, plugged into the mains as well as the phone line. They are all (reasonably) modern - no bells involved! Upstairs worked fine without a ring wire until I installed the ADSL Filter/Splitter Faceplate.

[Rik]

Try reverting to the standard faceplate without the ring wire. If that cures the problem, we know the cause, if it doesn't, it suggests a wiring or phone fault.

[nowster]

With the faceplate still in position, put a microfilter just on the upstairs phone. It's possible that it's injecting noise onto the line.

[Simon]

[johnpoliner]

Thanks for the suggestions - am rather busy at mo but will try them and report back!