This has got we worried - perhaps I'm wrong, but best to err on the side of caution ......,
Recently my Elektra has been dispensing erratic amounts of water on the presets that bear no relation to what they should and we have reverted to running "manual" and stopping the shot when we need to.
Something that I've noticed that is possibly related is, that on the completion of the shot and the solenoid shunt, there is a kinda "moan" from the pump (I think). - Almost like a "vacuum suck-back" if that makes any sense ?
I have no idea where to start with this and, as I have customers who depend on a reliable source of coffee, have decided to try to purchase a cheap "stand-in" machine to cover while I find out what's the score !!!!
Any hints at where to start would be gratefully appreciated.
Garp

That is odd. Erratic dosing volume could be the flow meter acting up but I have never heard of someone having a sucking sound form the machine. When was the last time you descaled the works? There is an over pressure valve that vents into the drip tray in the event the pressure in the pipes gets to high. If the solenoid was snapping shut before the pump kicked off it could groan when it opens to vent pressure. I doubt it is that but just a thought.

Dave, to be fair, it is certainly due a descale. Perhaps it's not a sucking noise, but certainly some kind of "overrun" sound from the pump.
I have just purchased a La Scala Carmen which has a small fault - once rectified, I shall swap machines and do a full tear-down descale on the Elektra.
Garp