sounds as IF your septic system is at risk. Mostly due to waterlogged condition or crud buildup in leech lines. There are people that have a machine they prod into the ground where the lines are,,,and it blows air at huge compressed psi and breaks up the grease /crud/ soap blocks. Think it blows styrofoam particles in there too to help.
but first things first,,,you well MAY have a silent leak in a toilet that seeps enough water it waterlogged the lines. TRY- turning off supply to toilet,,,look in tank,mark or visually note how full tank is,,come back hours later and see how full the tank is. Those flappers get a scum on them (here anyway)that allows alot of water to seep past them,but too little to hear. they also make a pill of dye origin you put in tank,let stand awhile and see if color is in bowl,,,MY way is better i think.
You should periodlicly flush the stool,hold the handle down while taking other hand and rub seating surface of your flapper,,if it is checked or cracked,replace,scummed,just rub it off ,,,,same with bottom lip where it sets on. AND no EWWWWWS cause its all clean water in there!!!
I didnt think I had a leak either till I was in basement and plastic pipe was telling me it sure enough was. I put my ear to my plastic soil pipe riser and could hear it plain as day then!!!
IF you are on a well and you hear or can tell it kicks on every now and then with ALL water off and none used lately,,,you have a leak,,,someplace,,, and stool is FIRST place to look
IF you have a clog in the line to the septic,,,a 50 foot tape with a roller ball on the end and enough run in the pipe to be SURE it is in the tank,,,then rotate the tape round and round and make it 'snap' which cleans off the walls pretty good. MOST lines clog right where it empties into the tank,,,they have an elbow there and junk floats till it builds up solid,,,and or soap scum solidifies.
I used to have alot of septics to maintain,,,guy showed me how to install 3/4 inch pipe in exact right spot to 'rod' this elbow open,,,with a cap on top so crap cant enter.
What kind of pipe from house to septic???Heavy wall Plastic??-good-Thin wall,orangeburg,, or other OLD stuff---maybe bad-- IF somebody installed pipe with a backhoe,,may have settle spots that clog easy!! OR I have seen pipes that settle from excess excavation right next to the tank and it 'shears' pipe right off the tank!!