Noise and poor dialling on ADSL enabled lines.

This has been a bit weird for some time.

I have a Panasoniuc analogue PABX, and it feeds currently, three lines.
Two BT, one VOIP via my interesting new router.

Now of the two actual BT lines, both have ADSL on them, and when I
connect the routers, no matter which filter I use I get both a low level
hiss, and occasionally, the inability of the exchange to recognise dial
tones correctly.

Removing the router makes the line noise-free and it dials correctly.
Two different routers and two different filters all show the same issues.

I've been scratching my head on this one.

Possible scenarios include

- the CO lines on the PABX going wonky in the presence of even small
amounts of broadband.

- rectifying contacts in some part of the wiring that are injecting
audio intermodulation products into the audio path, and upsetting it.

- general wiring pickup from the PABX and routers.


Broadband performance seems about as good as the attenuation figures
suggest it should be.

Obviously one starting point is to get a faceplate filter..what's the
absolutely top notch best one that is recommended?

Before I delve into further tests..