my 95 sc auto w/76000 miles is making a strange noise.it starts up&after a few seconds starts making a noise like a fog horn that comes out of the air box.when you give it gas it goes away.let off gas when coasting or idle it makes noise again.it is a constant noise.when you put in park,the rpms go up to 2000.shut it off & a big fog horn noise bellows out.any ideas ?thanks ,kevin