This is an abuse.
A recent Vatican document addresses this. Redemptionis Sacramentum discusses a number of different abuses and this is one.
[55.] In some placesthere has existed an abuse by which the Priest breaks the host at the time of the consecration in the Holy Mass. This abuse is contrary to the tradition of the Church. It is reprobated and is to be corrected with haste.
[73.] In the celebration of Holy Mass the breaking of the Eucharistic Bread – done only by the Priest celebrant, if necessary with the help of a Deacon or of a concelebrant – begins after the exchange of peace, while the Agnus Dei is being recited. For the gesture of breaking bread “carried out by Christ at the Last Supper, which in apostolic times gave the whole eucharistic action its name, signifies that the faithful, though they are many, are made one Body in the communion of the one Bread of Life who is Christ, who died and rose for the world’s salvation” (cf. 1 Cor 10,17). For this reason the rite must be carried out with great reverence. Even so, it should be brief. The abuse that has prevailed in some places, by which this rite is unnecessarily prolonged and given undue emphasis, with laypersons also helping in contradiction to the norms, should be corrected with all haste.
Here is a link to the entire document, Redemptionis Sacramentum, on the Vatican web site. Consider printing it and giving the entire thing to your priest. Have it handy when you talk to him.
In addition, Father Shannon Collins has a very good audio presentation from St. Joseph Communications covering the entire document. I highly recommend it. You can purchase it here.