Exhaust Fumes inside Accord

The first thing I would recommend is that you do a good inspection of your exhaust system, if it just started recently then your exhaust has developed a hole in it somewhere, make sure that you feel around all the piping and on top of the muffler and converter (just be careful because the medal can be sharp).

Another possibility is the entering of the fumes through the truck or rear of the car. Garfield is right and you should be able to detect the increase in noise from the exhaust system. But no matter, there is something in the way of an opening that is allowing the fumes to enter. Too early for rusted holes so check the possibility of fumes coming up through linkage to transmission, emergency brake, window not closing tight, trunk not closing tight, etc.