Volume Issues

Recently I changed out my alternator on a 2007 Saturn which has OnStar and when I finished, a few day later I noted that my onstar volume was very low and hard to hear (the commands were all there but barely audible).  I called OnStar and they could barely here me.  I then emailed them and they said to call their Tech Support which I did and the lady could not help me and suggested taking it to the dealer.  Is there something that anyone can think of that perhaps I am missing?  The volumn to the radio works perfect but when I put the phone to make a call or the onstar button, the volume is barely heard.  Turning the volume up does nothing to help.  Any ideas what I might look at or try next?