Coolant leak, but no idea from where...?!?

Was out of town this weekend but wanted to give you an update. No leaking anywhere around the studs. Read in another post here that this could be freeze plugs behind the motor (hidden by the tranny). Again, haven't verified this yet, but since there is no visible sign from above this seems to me to be a reasonable answer... Can't pull the tranny out anytime soon so my bandaid will be to replace the 15 lb cap with a 7 lb one to hopefully reduce the pressure a little bit. Thoughts?