Water pressure buildup causing water meter to turn
Heat and cold cause air expansion and contraction if your system is wet it may have a relief valve bumping excess pressure down a drain, If it is a dry system I would make sure the flapper at the wet/dry division is not leaking by this can cause all kinds of trouble but these are usually on large systems, smaller home health care systems I have experience with are wet and as the water in the plumbing heats the relief vents Down a drain. This is much better than a over pressure that starts leaking in the living space.