Hi,
We had new internal wiring and master socket installed in August & was happy with the 24Mbs speed I was getting.
However in the past few weeks it has dropped to 15Mbs with a lot of connection drops, i.e the speed is up and down, & it is causing buffering on sites such as You Tube & very slow file download speeds, downloading a large video or music file I am lucky to get 3Mbs & the speed drops right down to a few KB/s & then back up again.
I did the speed test on speedtest.net as your speed test is still down, & the ping was 17ms.
Have tried resetting the router, and there is no issues with crackling on the line.