Toilet bubbles when washing machine drains

You have a partial blockage downstream from the toilet. The solution would be to pull the toilet and snake the drain line from, there. Good luck, Tom

I agree with Tom but think you might find a clean out since you are in the basement. Look for one.

Bob has a good point, Look for a cleanout on one of the stack vents and not the clean out in the floor leaving the house. Good luck, Tom