When the bathtub upstairs is drained we get water splashing out of the floor drain in the basement. It seems to be specific to the tub - not sure if it is because of the amount of water draining at once, or some other reason, but we don't have any problems with the toilets, dishwasher or washing machine.

We've had the main drain snaked out from the drain and from the clean out several times and a blockage does not seem to be the problem. A camera was put in as well, and we were told that there is a bit of a dip in the pipe where waste can collect but it is probably not worth the cost/effort to fix. The problem occurs when this is clear as well.

Any ideas on what can be causing this? Could this be a venting problem?

Is the tub connected close to this drain? Does it overflow?