1997 Mercury Cougar

I have a noise kind of sounds like a fog horn. Its not all the time but is doing it more often now. The noise sounds like it is coming from the passenger side of the engine area. The sound is loud at the air filter area and when you remove the cover you can hear the noise coming down the hose that comes off the top side of the engine. If you are driving you can gas it and it quits, usually or if you turn it off, it will crank back uo and not be doing it.