does it have anything to do with the suction at all?
Yes, I would change your membranes. I just changed mine at almost 7 months...however, I had two sets of pump parts, so I suppose that is why they lasted a bit longer. I also find that if I have not connected my yellow Medela valves on "straight," the suction is a bit off. Sometimes, it is just a matter of repositioning the valve, if that makes sense. Also, I store my pump parts in the fridge between sessions and sometimes the milk residue kind of "freezes" or makes the membranes stick for the next session. So again, just repositioning the membranes sometimes is the trick.