I'd take components out of the loop until you find it. for example-
-First, run an hdmi straight from the receiver to the projector - no cat5 converter - and see if it fixes it. If it does, something's up with your converter or your cat5 cable.
-If it still does it then, try taking the receiver out of the loop
-If there's still a problem then, you should be direct connection of an hdmi cable from the source to the projector. You could try changing the hdmi cable at that point...
-If at that point, if you can confirm that you have multiple sources experiencing the same issue over, direct connected via hdmi, with multiple hdmi cables, and you're still having an issue, then it's likely a problem with the projector itself.