Grunting sounds from RO/DI unit

[FZ1Rider]

I've already sent a message to the vendor on this issue but since I don't expect a message back till the week I'll ask here to.

My RO/DI is making this grunting sounds every time it is shut off via a shut off valve. The unit is equiped with a auto shutoff unit. I think, but have not confirmed that it expels water every time it grunts (via the waste water line).

Any ideas what is happening or what I can do?

Thanks for the help,
Peter

 

[szwab]

haven't experienced this personally but an idea. it may be that there is air trapped somewhere in the unit and is getting compressed due to the water pressure and the valve being closed. similair to pipes knocking if you have ever heard that.