Sync speed has been gradually dropping.

[#1]

Hi,
My best sync speed has been gradually dropping from about 2500K a couple of months ago to 1760Kbps today.  I normally reboot the router regularly.  The current stats are:
noise margin upstream: 17 db
output power downstream: 16 db
attenuation upstream: 31 db
noise margin downstream: 11 db
output power upstream: 11 db
attenuation downstream: 56 db
I have tried changing the microfilter and used a different router but there is no significant difference in sync speed (actually this was a bit slower).  I only have one phone and no sky boxes or alarms to mess things up.  I have a very old BT master socket without a test socket.  I haven't made any changes to my setup (and I can't see how this would cause a slow and gradual change in the sync speed).
I have raised a ticket and PN say they can't find a specific fault but the sync speed should be higher.  I tried the BT quiet line test and there does not seem to be much noise on the line (just hiss from the phone itself I think).
I have never managed to get a BT speed test to complete.  It always get stuck at 96%!
Does anyone have any other ideas?

[#2]

Hi Mapletree,
Given that you're getting at least some hiss on your telephone line, it certainly wouldn't hurt to get something raised with BT Retail, or whoever your voice supplier is.

[#3]

I'm not sure if the hiss is introduced by the DECT handset & I don't have a spare phone to check it out.

[#4]

Asking them to test the line isn't going to cause any difficulties.
Worth trying.

[#5]

BT have done the line test and can't find anything wrong.  Sync speed now 1632Kbps 😞

[#6]

I'd expect to hear a steady very quiet gentle shhhhh type sound even with a corded phone. Can you not borrow one from someone for 10 minutes or so?

[#7]

I'm just getting a little white noise so this is probably normal.  I will borrow a phone soon but so few people seem to use them nowadays

[#8]

You can pick one up for literally a fiver if you can't find one to borrow

[#9]

You could take your phone to a friends house and listen to the quiet line test on their line.

[#10]

also it is a good idea to have a "normal" phone as any type of dect is useless in a power cut, a normal phone will still work