Update:
SFI engineer has just been. Showed him the RouterStats graph and the video before he started. He first reaction was "possible HR fault". Great I thought, this is what I want to hear.
Unfortunately it all went downhill from there. He stuck his equipment on the incoming pair, ran a multitude of tests with his equipment and confirmed the line is perfect. AC balance was perfect, minimal loss. He even checked the cable back from the PCP to the exchange.
He left his equipment plugged in for about 15 minutes to check for errors and I watched the screen. HEC / CRC and FEC all showing 0 on the downstream and upstream. This is the one time I want to see errors but unfortunately they just weren't there.
Pair quality test proved the line is "perfect". The only thing he did do is replace the jelly crimps with another type of crimp in the box where the drop wire comes in just before the NTE5. He did this because he'd been told the jelly crimps "could" cause interference but he'd never seen it.
The only other suggestion he could offer me is that the fault affecting me was affecting other people as well and that an engineer had been out prior to this visit and repaired whatever the fault was. The PCP is not in my road so I can't tell if an engineer had been out.
If the fault is still there, then I'll just wait until it gets really bad before I report it.
Oh well, I now expect a bill for the SFI visit as no fault was found despite showing the engineer the evidence.