Had to delete a track because of a doubling sound ??

I recently had to delete the bass drum channel , because it had an unknown “doubling” sound. The drummer said it was driving him nuts , and I of course thought HE was nuts , until I played his drum.

I checked routing , sends , inserts , no effects , and could find nothing. It appeared to be set up just like the other drums. We had just set the mics up , and we’re trying to get our first basic drum mix.

After 1/2 an hour of scratching my head , I finally removed the track , created a new mono track and renamed it bass drum. Problem solved. No more doubled sound , but I don’t know what happened.

I kept thinking without any effects causing this , and since I am doing all my monitoring through the DAW , I HAD to be hearing both the input and output , and was hearing the difference in latency , causing this doubling effect.
But , I couldn’t see how or why I would.

Anyone know ?

are you using the Control room for monitoring ?