My overflow drain has gas

[outtafocus]

I have found the water in my overflow constantly rises and falls. It goes up an inch higher than I want it, then drops and causes that horrible sucking sound. I am using the hoffer gurgle buster style plumbing.
The water then falls straight down into my sump, but as the above described "flushing" happens the water surges and burps out a large amount of air into the sump, causing splashing and sloshing.

I have read that because my plumbing drops straight down, it causes back pressure in the pipe. Which in turn causes the rising and falling and the burping.
What is the best solution to this issue? I was looking at changing the staight 1"pvc to the flexable style and running it at an angle into the sump. Will this even help?
What are your thoughts and ideas?
Thanks