Time Machine Drive active when Time Machine is not.

I'm running the latest Monterey 12.3 on an iMac-M1. I have Time Machine backing up to an external SoftRAID RAID 1 system (2 drives) attached by Thunderbolt. I find the drives are quite active at times when TM is not backing up. SoftRAID says that they would not be accessing the drive at that time. It can be active for quite a few minutes at a time. Any thoughts?