So I read this thread here:
Repairing a ULKA vibratory pump

and there were a few more scattered around and nobody has seemed to find a solution.

My PL41TQE was working fantastic for about a year, then I descaled it with vinegar, and now the pump goes quiet and the pressure drops Mid-Shot.
There's 3 noises really... Pump working no pressure - regular Pump working under load - then Very Quiet something's not right and the pressure dropped.

I pulled out the OPV and it looks fine. A little green, but not like it shouldn't work properly.
I pulled the pump apart and it practically looks pristine.

Is it the pump? Has anyone tried replacing the pump? Has that fixed the problem?

thanks!!!

Vibe pumps generally stop working altogether or the pressure drops right off...never seen one work for a time then not work. But, generally they do go really quiet when there is a down-stream blockage that stops water flow. Perhaps you've experienced this with a blind portafilter basket or a choked shot from too fine a grind. Is that the same sound you're hearing? If so, I'd run some descaler into the machine and let it sit a good long time, then purge. Maybe do it a few times. Hopefully, this will dissolve the troublesome bit(s) or at least make it small enough to pass. If this does not work, then I'd look downstream from the pump to find some bits of dislodged scale. Not sure about vinegar, although my did used to use this all the time in his retirement career as a small appliance serviceman. I'd go for a descaler recommended by the manufacturer of your machine, or at least a well-known one.

Thanks! I'll try another descale.
It's not the same sound as the choked/Backflush sound it used to make.
That was quieter but you could hear it working and fighting the pressure.
This gets quiet. Like it's still running, but just barely. Not like it's fighting, but more like it gave up
Yeah, It may well be a piece of scale stuck in one of the boiler outlets.
I'd had it for about a year before I descaled it.

Yeah, unless you left the vinegar in there for a week or something, most likely pump not physically damaged.