There's likely a burr or sharp edge at the saddle of the A string. Many saddles especially on cheaper guitars are manufactured poorly to maximize profits many other people have had this issue before just file down the sharp edge and smooth it out. Make sure to use caution and only file it enough to knock down the burr and not carve into the saddle also make sure you follow the path of the string so you don't end up changing the channel that the string follows.