every other time i play the A string it makes a wierd screech sound at the beggining then finally the normal note. what sould i do

This could be a few things. One, make sure your bow is extremely well rosined. If its not, it may not come out clear at first. Also, there should be come rosin on your strings, it helps start the note more clearly.
You may also be playing too close to the bridge. Try moving the bow a lil farther up. Of course, you need to play near the bridge when you get into thumb position, but up through about 5th position, you dont need to be too close.

Let me know if it helps!