Apologies for resurrecting my old post.... since last posting I've been monitoring the line and found that nothing has improved the daily dips in SNRM. I've tried things like changing the plug sockets, using a different modem (Zyxel 8924) instead of the HG612 and monitoring the line when we've been on holiday with only the modem, Pi and Router powered up the in the house.
Yesterday I put the HG612 back, and also replaced the gel crimps on the incoming feed. This did have the effect of increasing the SNRM from 5.8 to 7.6. However, the regular dips in SNRM continue to occur, so not much chance of DLM relenting. I really have no idea what's causing it.
BT called me yesterday as my contract is up for renewal. They were convinced I could get over 40mb, and wanted me to try their new and improved technical support team. They duly put me through, and unsurprisingly the person I spoke with decided there was nothing wrong with my line, despite the 10mb drop in speed over one night last year. He felt the best course of action would be to send me a new home hub.
So, as the BT renewal price for being a valid customer is £12/month more expensive than their 'new' customer deals, and deals offered by pretty much every other supplier I'm now looking to move supplier.
Would there be any benefit in me requesting the new provider supply me with a new line?