Recently I've noticed a strong septic odor emanating from the toilet in my basement bathroom. It appears that the odor, regardless of how clean the toilet is, fails to go away. Could this be a problem in the pipes? I have never had a problem w/clogging etc. I have a shower in the same bathroom but no odor seems to be coming from its drain pipe. The sink does not seem to have any odor either. Please advise. Do I need to call a plumber?? Thanks.