Paul
I've never heard of anything like this. Are you sure the haemodiafiltration unit is not faulty?
I doubt whether the filtration causes enough of change in physiological signals to cause this kind of interference.
I would suspect something like an insulation failure on the pump mechanisms which could give rise to electromagnetic noise - this is more likely. Check to see if the interference is there when the pumps are not activated , and when the machine is not activated. Is the insulation breaking down due to heat/spillages etc. I would go down this road first until you are sure the insulation resistances, and leakage currents are within expected norms. Also check that earth connections (leakage paths) from the motors are good.
hope this helps.
