This is an odd request; but I wonder if any of you know anything about plumbing. My toilet functions correctly for the most part, but has recently developed a quirk that I cannot fix. When I flush the toilet, it drains properly, refills, and then slowly drains completely before a few "glup glup glup" burps, and only a few inches of water remain. Previously it would drain to about half full and remain at that level. I'm pretty good with toilets, but I can't figure out what could cause this. Any suggestions?