Originally Posted by audiotech
I'm not saying that this is the cause of your problem, but many of the drums in the Gretsch Renown series have had trouble with loose vent holes. If you want to dismiss this as the problem, just put you finger over the vent hole and hit the drum. Two of my rack toms had this problem when they were new.
Totally forgot about this, it might be your issue as well. Unfortunately there are a lot of nonspecific metallic ringing sounds you can make on a drumset.