Please bare with me as i ask this question. I live in tennessee. the last week has been unusally cold here. woke up 2 days ago to find water in both my bath tubs. plunged and plunged, heard like a gulp gulp sound. lots of water bubbles rising to top of drain. ok, here goes by the end of the day all water was gone, daughter used bathroom and backed up into both tubs, not toilets or sinks tho, woke up water gone again. washed dishes took shower still all is good, then did one load of laundry and boom water again in both tubs. where my septic is it is dry no leakage, then on to field line area, dry but ground is frozen solid. cleaned out vent stacks, all looked good.could thius be a septic issue or field line issue? Maybe frozen? plus for some reason my water pressure in house starts off good then drops down to a trickle then back up. could this all be connected?