Noise Margin What's normal??

[#1]

I've been tracking my noise margin for the past few days because of intermittent losses of sync.
I notice that at around 5pm this evening the noise margin suddenly dropped by 2dB. (See attached graph)
The only thing that might have triggered it was the hot water boiler starting up. So I switched the boiler off but the margin did not recover.
From that time, the noise margin has been up and down like a bride's nightie! I think the cause may well be external to my house but wouldn't know where or how to start tracing it.
Does anyone know whether this is normal?
Can anyone suggest a procedure which would help me find the cause?

[#2]

That graph is not too untypical for many people, a lot of electical things get switched on in the neighbourhood as people come home from work, start cooking, switch on the TV etc.
Nothing really to worry about.

[#3]

The sawteeth just reflect that the router only resolves noise margin to the nearest ½dB. Small variations in the value round 6¼dB and (later) 5¾dB cause the apparent spikes. I suspect noise margin will suddenly increase again by 2dB when appliances are turned off at bedtime.

[#4]

spraxyt - you beat me to posting the answer to my own question.
Overnight the minimum noise margin was recorded as 4.5dB. I noticed a 2dB increase at 1am - exactly 8 hours after the drop of 2dB at 5pm yesterday.
The main thrust of my post was to ascertain whether others were noticing similar events, how they went about investigating these and were they successful in finding/resolving the 'problem'.
The stats for my line are attached. Of the 51 error seconds, 24 happened at 5pm last night so something upset my line at that time. FECs are a bit high but as they are corrected I don't think they are anything to worry about. CRCs/HECs are not too bad either - I can live with that level.

[#5]

Hi MrT,
I'd say your graphing looks normal as the other members have suggested.  Within plus or minus 3dB is quite normal.

[#6]

If the noise margin steps down and up occur at fixed times each day then a device on a timer is the obvious culprit. Random timed events are harder to isolate, easier if the electronic noise arises in your own property but needs cooperative neighbours if it's from elsewhere.
I suspect a spectrum analyser would be needed for detailed investigation/analysis. I think the Wi-Spy products from MetaGeek would do the job, but they are not cheap.

[#7]

Have got some interesting results today. The noise margin was constant at 7dB from 10am until 3:45pm. It then started 'dancing' between 6.5dB and 7dB.
Oh NO! I've just checked RouterStats and note that DSL went down at 17:17. It restarted immediately at exactly the same speed - 3776 and a margin of 7.0. Confused - you bet I am! Router Stats attached.
My hot water boiler starts up at about 17:00, so would not have been responsible for the fluctuating margin but may well have had something to do with the loss of sync. Maybe I'll try starting it at a different time tomorrow. Having said that it comes on between 6:30 and 8am anyway. So maybe that's just a red herring.
With the router's uptime reset to zero, does this mean that my 72 hours restarts as well even thought the speed has not changed? 
It must have been the shock of seeing the price of the spectrum analyser. 
Perhaps it's time to try another router - I see there are refurbed Netgear DG834Gs available on eBay for £20.

[#8]

If I was you I would try and find a SpeedTouch 585v6. My connection used to drop a lot due to changes in SNR margin but since I have got it it has transformed my connection. Make sure you ask for an unlocked one so if you want to you can tweak the SNR margin later on.

[#9]

My current router is a Thomson TG585v7 so I thought I'd try something different. I've read several good reports, mainly on this Forum, about the Netgear DG834G v3 so I thought I might splash out £20 on a refurbed one on eBay. Given that my sync speed is generally below 4000Kbps, I see no reason to buy a N router.