A humming/buzzing noise come and goes when I turn on the heat defrost or heat floor setting, however the noise does not come on when I turn on the dash vent heat setting. Along with the noise, which has been going on for about two weeks, the engine has now started to lag whenever the noise is present, causing me to not use the defrost or floor setting for fear of causing damage. I just watched a video on youtube about replacing the blower motor, but this does not seem to be the problem to me, as the noise does appear to come from the dash but from the engine area. Thank you for your help.