The automated tests is an inital way of trying to see a fault, but it dosn't beat going on the line and testing with a 9083 or a hawk.
Admititly a hr fault can sometime become elusive, and typicaly can involve corrosion somewhere, although from what you've stated it seems this was ruled out.
As for the snr problems then there is a whole miriad of possibilties as to the cause.
A hr fault would normaly show it self on your normal voice telephony. I had one saturday. contractors fitting new barge board & soffit, damaged the drop wire and repaired it by twisting the copper wires together, and that it. open to the elements, so when i get there it's corroded badly, and a noisy line. Remade the joint with a proper closure and crimps. nice quiet line and the broadband which would bearly touch 1mb is now running at 7.5mb. yet the line tested as "line test ok".
A hr should show up on aline test but dosn;t alway's, the engineer should be able to spot it with their test gear if close enough to the fault, but typialy clipping the butt phone on will give it away that there's a hr on the line.
The problem with broadband faults is you can't lock yourself on one type of cause, got to keep a very open mind
