I assume that this noise is only after superimposing the DSL filters at the exchange and Customer premises. . If so, YETO may try with local engineers to get the DSL wedged out for test purpose on either side.
If still noise persists, it is due to cable being leaky or due to power induction.
otherwise, the Central office can oblige a spare set of filters, what they call as port change. It can't be that the Telecom and DSL providers cant solve it.
as rightly pointed out by RODALCO, any phone instrument installed before the splitter is likely to have the DSL noise. we are expected to have telephone instruments only after the splitter, at the phone jack of splitter.