When testing the return line ( jacuzzi face plate ) with air, I hear a gurguling noise above the return behind the liner. I removed the face plate, left the plug in, and induced air. Bubbles came out the top screw hole. What is happening ?

I could be way off but:

Jacuzzi makes therapy fittings along with standard returns. Possibly pool builder didn't extend air pipe for therapy above deck or into deck?