Hey Roy,
I’m joining late so forgive me if I missed something that was already said.
I think you have two issues.
The hiss is pretty clear and easy—especially since you only have it with the steam boiler. That boiler has a vacuum relief valve, and it’s an easy fix. There’s an o-ring, size 007 if memory serves. Take off the top part (that the needle protrudes through) and clean it all up and replace the o-ring with a new one of high-temp silicone. Buy extras, this is a relatively frequent repair (couple times a year running my machine 12 hours a day).
The pump thing seems unrelated to me, and seems like probably a leak in the pump itself. The water level in the brew boiler is falling, and when the sensor detects that, it has the pump cycle on to refill. The vibe pumps do wear, and so that’s my guess. Also not uncommon to have those wear out as they are a simple metal piston.
Other than that I’d look for leaks that allow water level to fall.
Oh, and as to the other safety valve (on top of the steam boiler), it’s an over-pressure valve also and if it goes, you’ll know it—sounds like a freight train coming through for a few seconds, then it reseats and gets ready to scare the hell out of you again. In my experience, it’s not a gentle hiss. ;)
Hope some of that helps, and forgive me if anything is misstated as I’m working from memory at the moment.