Hi i purchased a new townhouse (end unit) a little over a year ago. It is 2 1/2 baths, anyways when i flush one toilet the other 2 make a huge bubble that sometimes splashes the seat. I have ran a 25ft. snake down every toilet and found nothing. Also i have no problems with any sinks or bathtubs making any sounds or backing up. Does this have to be a vent issue? My townhome is 3 floors so i cant even get on the roof to look in the vent. im really dreading paying a plumber a crazy amount to fix this issue. any kind of input would be appreciated. thank you