That is strange, and I am sure infuriating. I have a Leakshield and am running Aquasuite X.84 and Leakshield Firmware version 1022. The Leakshield Firmware was updated with Aquasuite X.83. The update notes say Bug Fix – Alarm Actions and Update: Pump speed increased (reduced pumping times). Neither should cause what you are observing. It could be a coincidence that your Leakshield pressure relief valve happened to get stuck closed or fail at the same time you did the update, but that seems unlikely. Hopefully, someone from Aquacomputer will respond. If they don’t, send an email to support.

Quoted from "spinelli"

Do you know if it's possible to revert to older firmware somehow? Then I can test it again with older firmware. But it literally started IMMEDIATELY after the update so, ya, the chances of the update/s not having anything to do with it are like astronimical.

I have seen many posts requesting a regression of Aquasuite, and the answer has always been NO. If the update included a firmware update, the answer is double NO. Since no one from Aquacomputer seems to be responding to this thread, I suggest emailing support. This forum is not really a support forum. Its more of a community forum that the Aquacomputer guys sometimes will post in, but no guarantee. If you want a response from them about what may have caused this and if there is any chance of regressing Aquasuite and flashing the previous firmware version, send an email to support. There is a SUPPORT button in the upper right side of the forum window. If you click on it a page opens with the email address for support. Here it is.
Please send email inquiries to: support@aqua-computer.de

What they will probably say is that if the updated Aquasuite or updated Leakshield firmware was causing your problem, they would be flooded with posts and emails reporting the same thing. Since they are not getting tons of reports of the same problem, that means the updates did not cause it and it is something specific to your system. I don't mean to discourage you, but I have seen them say this before, and it is a fair point. You could ask them if the pressure release valve is something that you can replace, and if they can send you one. They are pretty good about providing replacement parts. Good luck!

There have been no recent changes to how LEAKSHIELD works, so I think the problem is more likely to be a silly coincidence. As Speedy-VI already mentioned, if there were a general problem, we would have received countless reports by now, but that is not the case.

If not already done, the first thing you should try is to reset LEAKSHIELD to its factory defaults. This is done in the system tab. When you start the test mode, wait a moment and abort it, you should have a quick feedback if the problem is still there.

The weird noise that you hear is very likely the valve which would indicate that it seems to be working. Since the negative pressure is not getting released, it could be maybe a problem with a clogged membrane. You can check that in the system tab of LEAKSHIELD. There is a diagnosis button that will bring up a new window with some test options. You will have to perform the test where LEAKSHIELD has to be removed from the loop. Make sure to grab the glass tube when you unscrew LEAKSHIELD to avoid that it comes loose at the base. In this test, LEAKSHIELD simply pumps the air without resistance, creating a slight vacuum internally. If a threshold value is exceeded (wil be shown), this is usually a clear indication that the membrane is clogged, which can lead to all kinds of problems.