Have a strange fault - on our landline - if we are using the internet to any extent ie downloading video etc, it prevents people from hearing us on our landline - or at least we are unintelligible? Tested this yesterday. Phone someone back and stopped any internet downloads and they could hear me? but they couldn't earlier when I was downloading.

I tired a different filter and same outcome?

There is only one phone jack/line in the house. It is quite a thin phone cable (not cat5)

Before I call faults, is it more likely to be a problem with our internal wiring

We are getting an electrician in next week to install the line/jack in a different place as where it is, there is no power point nearby for the cordless phone

We did have a few issues  a few weeks back and chorus repaired the cable on the street somewhere - but this issue wouldn't be due to a faultly line on the street would it?

Anything else I should test first?