After our return from a week long absence, when we flushed any of our toilets we could hear a long drawn out moan coming from the toilet. It does not come from the tank but seems to becoming from the house itself.

Any suggestion will be appreciated

Did this "moan" happen as the toilet was filling or when it was first flushed?

After our return from a week long absence, when we flushed any of our toilets we could hear a long drawn out moan coming from the toilet. It does not come from the tank but seems to becoming from the house itself.

Any suggestion will be appreciated
The noise occurs when either of our toilets are flushed. Probably as the tank is completing its refill.