loud sucking sound
 

I just plumbed by first tank and unfortunatly my overflow is sucking a lot of air making a really loud toilet flushing sound.

One option I have considered is to modify it using a dursal (sp.) type overflow.

I would prefer a simpler solution as to do this would require me getting a new bulk head. (the current one is glued in).

When I plug up the hole it backs the water up and stops sucking air. I am not sure this is such a great idea as it would be more prone to blockage.

Any suggestions?

Sounds like the hole for your durso is too small.

Here is a link for DIY Durso Standpipes.

Try backing the flow into the tank off a bit. Like Joe Reefer said, it sounds like you have a little too much goin in, and the overflow cant keep up. If you throttle back the returns slightly, you should notice a difference

No, I mean the hole in the top cap of the durso. Too much flow could also be the problem though.