Who should I call to investigate. Does not smell like gas. Started quickly

Hi Magick

Look around the basement for any unused drains... like a toilet, sink or shower that has not been used in a long time. Here, you could have a trap that has dried up and is allowing sewer gasses into the home. If this is the case, simply pour some water down the unused drain or fixture and that will resolve the issue. If you plan on continuing to not use the problem fixture or drain, you could also pour some mineral oil into the drain which will create a seal that will stop sewer gasses from coming into the home and the oil will not evaporate away.

Also, look for a floor drain or a cap that has come loose... here, you would fill the drain as above or you would cap the drain if needed.

If you have a condensing boiler that drains the condensate into the washing machine drain that could also cause odors... clean the interior of the washing machine drain pipe and replace the condensate to fix this if it is the problem.

Otherwise, if none of these are the issue, I would call a local plumber in... could be a sewage ejector gas odor, could be a venting odor, etc. etc. etc...

Back to you...

Mark