The internal wiring is one of the most likely points where problems with dsl will be picked up from and in certain cases could cause the problem your having.
What ever the problem with broadband any one may have the first thing to try whenever possible is to connect via the test socket in the master socket (nte) as removing the face plate disconnects any internal wiring so take this out of the equation.
If then you get a better result you can either take certain actions to disconnect the offending wiring from the dsl signal.
The problem with a throttleback situation if thats what you have is the current stats seem ok so its difficult to tell has the problem dissapeared or is it intermitent and about to strike again. in which case trying to find out if the internal wiring is causing the problem become hit or miss. Idealy you'll need to catch things as the stats go squirly and then try a comparison with and without the internal wiring connected. Unfortunately you situation if my assumptions are correct becomes exteamley infuriating.
If your stats stay stable then get you isp to check if there is a throttle back situation which can be nudged off. Hopefully if it was a one off (or christmas decorations nearby, so roll on next year
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If anything has caused some venerability to the problem then the most likely cause would be the internal wiring. It can be perfectly good materials and fitted absolutely correctly, yet still act as an antennea ready to pick up the right interference. Some people fit the full dsl ssfp front plate even though at the time it makes no difference to the performance, but it guards against any future potential problem from the internal wiring.
If your going to look at the internal wiring the things to look out for. Clean intenals of the sockets, no corrosion/moisture. anything verdegre (copper green fuzzy coatings anywhere)
The wires terminated don;t have "tails" that is a long excess of wire sicking out of the otherside of the termination. The IDC style terminations (the type where the wire is pushed into a slot to make the connection.) have a slight step on the white plastic moulding which holds the wires. the excess wire is ment to be trimmed to about the length of the step. anything longer can act like an antennea.
Any spare wire are not "coiled back" Its an old practice to neatly tidy things up where the spare pairs of wires are wound around the end of the cable so they stay neatly out of the way. Now a days i the disgital age this can pick up signale on the used pair of wires and amplifi the signal back within the cable causing problems. if you find this unwind them.
Coiled wires in nice neat loops, tidy but a good loop antennea, flatted the loops so any spare wires just go back and forth a couple of times.
Inetnal cable running paralell to mains cables foa any length within 50mm. as this increases the amount of noise picked up from any mains noise, comms and power cable s best runa as far apart if running along the same route.
Power cables coiled round and around particuarly near any comms cables, this amplifies any noise via the mains. Tidy but can be a problem
You dsl cable connecting your router to the socket, is it coiled up, unravel it and avoid runnig it along side any other cables for any long lenght
Is there any thing plugged into the telephony thats unfiltered, could you have an external bell hardwired or an alarm system.
Star wiring, that is any extention wiring comming off the lead-in before the master socket. Defeates the object of disconnecting the face plate on an nte to diagnose any problems.
Are all the extention socket with a capacitor. this idealy should only be in the nte and the microfilters. If thing have been wired up using only 2 wires and no bell wire after the master socket then a socket with capacitor is needed to get the phone there to ring, unfortunately can cause a capacitance inbalance so making the internal wiring more likely to behave as a radio.
