Odd occurance last night. Wife was running the wash machine. Kid flushes the downstairs toilet and it overflows on the hardwood floors.

Its odd because it has soapy suds in the water, like its backing up from the adjoining room where the wash machine is. Anyway, I snake it myself with a hand snake about 20 feet in. Still didn't solve the problem. It eventually drained down, slowly..
We had the septic pumped out 3 years ago. It has 3 chambers and a main tank. I checked the main tank of the septic system and its at a normal level. I was going to dig up one of the 3 chambers to see what their level status was today before calling either the plummer or the Septic guys.
Any clue as to what could be happening? I don't want to pay both a plummer and a Septic guy if I don't have to.