My upstairs bathroom is acting up. If you shower, the toilet bubbles,. If you run one sink, the other sink is fine. The toilet flushes only if no water has been used in a while. Everything downstairs is fine. Bath, washing machine, kitchen. We had roto rooter. $500 and everything was fine. Septic is pumped every other year. Pumped two weeks ago and no problems. Plumber($125) came and everything acted fine. We could not replicate problem. Prblem started again next day. Should I have someone look at my vent? It is a 250 year old house with very high roof.