Loyalyid, you are absolutely not “too over mannered”; eating silently and with one’s mouth closed is polite courtesy and should not be de-emphasized. However, I agree with oomis- I would rejoice if we had nothing else to worry about but this!
Incidentally, did anyone else read the Mrs. Piggle-Wiggle series as a child? One of those books has a very cute story addressing table manners. If I remember correctly, her method of correcting bad habits involved the assistance of a pet called Lester the pig. I used to love those books!