It sounds like I am just about as new as you, but I have had the same problem and here is what has helped me. I start with long steady single notes, as long as you can get them before they start to wobble. When I get a good long note, I began to break them up at 4 second intervals. Then when that is steady and the notes sound clean from each time, I slowly get faster cutting the time in half each time I consistently get clean notes. I do this about 15 minutes at the start of each practice.
Also like Morgan suggested your jaw might be moving or in my case pressing too hard against your lower lip. I've found the best way to check for this is to slur into the notes that I squawk on and try and notice where my jaw is in relation to my lower lip, then try and remember that when playing said note on it's own. It might help you keep your jaw more properly positioned.
Like I sad I am very new myself, but I hope some of this might help.