Noise on phone line

[#1]

I do hope someone can help me as I'm going around in circles. I upgraded to MAX about 4 weeks ago and all has been fine. Then yesterday afternoon, I plugged in my dial-up modem to send a fax and then unplugged it again. Ever since, I've had an awful hiss and sometimes squeal on the phone line to the point that I can't hear the conversation. If I unplug my router the line is perfect.
I did the Fault Checker and the BT Test thing and because the speed isn't an issue, Plusnet are saying nothing can be done from their end. Incidentally, my speed dropped to about 400kbps last night but it's back up to around 6Mbps now so I'm not concerned about the speed.
I rang BT and they tested the line and said it was OK but was showing an 'anomoly in my house'. They advised me to plug my router into the master phone socket to eliminate any possible problems with the internal wiring. I did this and I'm still having the problem.
I've changed out all my filters, I've unplugged phones, Sky, etc. one by one to try and eliminate equipment problems. I don't have a spare broadband router or modem to try.
I seem to have been left high and dry by both Plusnet and BT on this issue and don't know how to proceed. BT said that if they sent an engineer, I'd have to pay £116 and all they'd do is disconnect my broadband saying that's the problem. Huh? Can anyone offer any help please?

[#2]

They advised me to plug my router into the master phone socket to eliminate any possible problems with the internal wiring. I did this and I'm still having the problem.
Hmmm...could of course be a coincidence that the two events happened together. And you might have more than one bad filter. 
Did you plug into the front of the master socket or into the test socket inside the master socket?
If you plug a proven-good filter into the inner socket (you need to take off the faceplate to do so) with the router and phone plugged into the filter in the usual way, do you still get squealing?

[#3]

Thank you for the reply. Unfortunately, this hasn't solved the problem. I'm still getting the hiss, the squealing was intermittent anyway so not sure if this is still a problem or not.
I have 4 filters and only need 2 so have swapped these around. I doubt very much that all filters would become problematic at once.
Do you think the router has suddenly gone wrong. Are there any statistics that I can supply that would indicate this? I'm afraid I'm not technical enough to understand what it all means.

[#4]

Here's a link to my router's stats if it helps:
http://www.barnes.plus.com/plusnet/stats26907.jpg

[#5]

Suggestion: order from ADSLNation (www.adslnation.com) either an XTE-2005 filtered faceplate (which replaces the front of your master socket) or an XF-1e microfilter.
As far as I know, these don't just filter the 'phone' side but also prevent unwanted router signals from hitting the phone line (routers themselves are pretty tolerant of phones, but  these filters should stop unwanted squawks from your router if it is sick).

[#6]

Thank you for your replies. Here's an update.
Didn't get a chance to investigate things further last night but mysteriously the problem seems to have gone away all by itself this morning, thus surely proving that it had nothing to do with my wiring or equipment, I would have thought.
Still no-one at Plusnet or BT wants to accept responsibility. Hmm.
Oh, we do seem to have had a power cut in the middle of the night. Perhaps that did it. Computers and router are all unplugged at night anyway!

[#7]

Hi Annie,
The hissing on your line is extremely, very, incredibly, highly, immensely and remarkably unlikely to be caused by PlusNet or BT Wholesale.
I would suggest that it was likely to have been a BT Retail fault, now fixed.

[#8]

Speaking from past experience I understand that a bad junction in the phone line could have caused this.
In my case at home it was cleared up as a voice fault.