We just had an oil change & full engine flush we noticed major improovments w/the van. Our heat acts funny it takes a long time to heat up & @ times will just blow cold air. Today my husband drove home from work everything was fine, when he pulled in the garage & parker he heard a loud blowing/humming/buzzing sound coming from under the hood. The heat was turned off, radio off. Was curious what this could be from? He said it almost sounds like a computor that's on and just sitting/running.