Loud Howling on right side

We have 2005 Freestar, which has howling noise to the right, Ford technicians thought it was the air handler which we replaced, but no difference. Usually gets loud when van warms up, but immediately goes away when foot on accelerator, we've replaced water pump too as that's what else was suggested.
Any suggestions as to what could be causing this annoying noise?

If you remove the drivebelt and start the engine (do this for no longer than 30-60 seconds) does the noise go away?

BTW do you have a Freestar? The last Windstar model year is 2003.

Yup you are right it's Freestar we have..thanks will try that and see if noise goes away. Thx

Yup you are right it's Freestar we have..thanks will try that and see if noise goes away. Thx

Post back and let us know. We're just trying to narrow it down. If it goes away when you remove the belt then we know its something the belt drives causing the issue. (If not, fire the mechanic who told you it was the water pump because they should have done this test first!)

I've got two guesses .... (1) old/dry synchronizer assembly ...(2) broken internal parts in intake manifold.

When I'm having trouble identifing the source of an engine noise, I find that my auto sthethescope is extreemely helpful. Normally the scope is use to hear internal pings, knocks, taps and growls by putting the metal wand on the engine at various locations while running. However it is also very helpful to remove the diaphragm assembly from the hose, then use the hose to isolate the source of a whirr, hiss, or buzz. It wasn't very expensive (<$20) and well worth the price.

Of course, use extreme caution any time you're working around a running engine. Anything that gets caught in the spinning belts and pulleys can lead to a serious injury.

'Howling' usually indicates a bearing problem - perhaps PS pump, or alternator etc. I'd take the belt off momentarily as earlier suggested, see if that changes anything and go from there.

On the other hand, if belt removal doesn't provide a clue and the howling remains, I'm wondering could it be a vacuum leak? although that's usually more of a 'whistling' noise, but it could easily be misinterpreted as a howl.