Most probably is drone cells in the comb drawn inbetween the frames between stacked hive boxes. Very common in spring. Swarm Queen cells are usually at the bottom bar of the frames, drones in the space inbetween the bottom bars of top box and the top bars of the bottom box, in the space between the boxes. Most commonly. Sometimes queen cells can be found wherever you happen to find them.
I've been keeping a few hives for the past 20-25 years, and no longer treatment free as I got tired of the losses.