Pop!

Took my Dart to irwindale Thursday night TnT. It has stroked 440,Indy heads,intake,modest roller,T&D rockers,blah,blah. Make a pass,at the line about 175 degrees. Finish at about 185. Looking it over and I hear a sharp pop metallic noise. 5,10 more minutes hear it again. Can't find anything. Didn't look that hard. Cars running quicker each pass. Any ideas? Thanks.