I worked for AT&T for 24 years. I am VERY versed on DSL. Was a DSL Technician. Was going to say, if they found the problem "down the road", it was more then likely Bridge Tap. Probably a "floater", a drop wire tied down to your F2 pair. The signal goes down the extra wire, and bounces back on itself degrading the signal. Need a TDR meter to locate issues like that.