probably an actuator vacuum operated to open/close heat vents
Your description of the problem sounds a little vague, but it sounds like you are describing a vacuum hose leak someplace behind the dashboard. Probably something to do with the climate control system, like a blend door activator.
If the noise is coming from the rear then the bushing is broken.
You may have a brake booster that is leaking. The diaphragm may be busted. You will need to remove the brake booster vacuum hose and do a vacuum bleed down test. If the booster will not hold vacuum it needs replacing.
The noise of a vacuum may appear very soothing to you.
Check your belt cover sometimes it looks like is on the right way but is not and also check you belt play and tensioner try moving it with your hand.
I had a noise in the front end of my 2004 Mountaineer similar to what you described and it was front wheel bearings on the passenger side. $291.
you need a new starter motor
Its probably your air intake.... check under the hood and see if it runs to the inside of your passenger side fender.... mine does and it sounds like the noise your describing
This may sound funny but check the pcv valve, it sounds like you have too much crankcase pressure and possibly a vacuum problem. check all the vacuum hoses, a disconnected or cracked one will make a loud sucking noise, skipping can be a symptom of low vacuum pressure as well.
The Grinding noise in the passenger rear of a 2002 Explorer is most likely either a bad wheel bearing, or a brake problem. Check the brakes then the bearing to find the cause.
Sounds like one of the fan blades are loose, or bent or out of balance. By saying whopping noise points to a problem with uneven air currents.
sounds like either your a problem with your timing change or your airflow or timing