We are getting more air suction thru the upper vent grille than we are thru the grease vents over the stove. I took the vent grille off and it was full of grease, where as the ones over the stove there was nothing. I need to know what is wrong because it does blow grease in my kitchen. I know this has not worked properly since I bought it because there ahs always been a grease build up in the upper vent grille. There is practically no air flow to the grease filters over the stove. Please let me know what I can do.