Need help from Simplus FFM users (and others)

Hi everyone, long time no post. Hope you are all well! So here is my problem: the nice folks at cpap.com have shipped me two Simplus Full Face masks. The first was a new order, the second one a replacement. However, I am having the same problem with both masks. This is a problem I am *not* having with my current Simplus. Here are the symptoms:

1) Put mask on, fire up machine, getting a hissing sound.
2) It is *not* a leak I am feeling anywhere, and adjusting the cushion does nothing to stop the hissing.
3) If a cup my ears the hissing seems to be coming from the left side, but that's not certain.
3) When I put a new cushion (the ones that came with the new masks) on my old frame, the hissing goes away completely.
4) I use a wonderful Padacheek mask liner to stop leaks around the bridge of my nose, but either using or not using the liner with the new masks has no effect.

So could this be some sort of internal leak related to the connection between the cushion and the frame, or perhaps something is going on with the little rubber valve that goes up and down? Pardon my poor nomenclature. The fact that I am get the hissing to go away using the new cushion/old frame combo seems to indicate to me that the frame is the problem, but I really don't exactly what is going on. Ideas anyone? Thanks!!