I know you wanted to emphasize distracting them with grenades, but currently there is no way to sneak by them by moving silently because they bang all the time like crazy. I remember in 2012 release, one of the tentacles (the only furthest from me) DID enter an idle stance and it didn’t bang the floors, but a slight itch of movement provoked it into banging again. So it seems that idle behavior is actually coded and intended, but somehow not working correctly.
Yes. It doesn’t work as it did in original Half-Life. You can’t sneak past them now. I finally figured out to just throw a grenade to slightly distract them while running like hell to the nearest ladder. Throw another grenade and repeat until you get out.
If this is the intended way to defeat get past them I’m dissapointed.
Yes, I can also confirm that the tentacles’ AI isn’t performing correctly. At least, not like in the original HL.
Please, fix their AI to actually ignore you while you sneak !!!
This has been one of the ongoing issues, every time it gets fixed something else changes and it gets messed up again. We really have been trying to squash all the AI bugs, but they keep popping up from time to time.
Well, you have to fix the AI bugs again 
Also, fix the vortiguants’ behaviour. They often get stuck / frozen / do not move nor attack anymore :\ Really odd. In the 2012 mod version, they didn’t have any problem. They moved towards you, attacked you non-stop 
These two are known bugs. Please try searching to see if they’ve already been reported.
Thanks.