Brand new engine, heard a clicking noise while reving..
 

i recently had to have a new engine installed into my 04 auto rx8 due to lose of pressure. i jut got it back today and have been driving it around all day, when i got to the house, i decided to rev it a couple of times, while it was reving, i head a single click not to loud sounded kinda like the a/c click, but my a/c wasnt on. i reved it to about 7 7.5 rpm when it happened. Could this clickin noise be a problem with the new engine? or was it just maybe the engine breaking in? or maybe something i dont know about? any information at all or ideas on what it could be would be very helpful... thank you