Please forgive this lengthy post - especially from a newcomer!

I have an '04 Expy XLT (5.4, 4x4, tow package) with 110k miles on it. Just last weekend it started making a noise that is both hard to describe and impossible to reproduce on demand. It has only happened at freeway speeds and the wind noise generally makes it hard to isolate this noise from others. To me it sounds like a suction noise or maybe a higher-pitched rattling.

The first time I heard it I had the cruise set at 65 and we were near the top of an overpass (moderate incline). I tapped the brakes and it stopped. A mile or two later it happened again, this time without cruise control. Again it stopped when I let off the gas. After the third time, I pulled off the highway and checked for any road debris caught underneath - nothing.

The noise continued intermittently the entire trip between Phoenix and Flagstaff, and then back (~200 miles). I discovered that once I hear it, I can stop the noise by simply letting off the gas (this works EVERY time). If I don't stop it, the noise will generally increase in volume, and on several occasions a "thumping" could be felt in the floor by both the driver and front passenger. Here are my other observations:
The noise:

• has not occurred below 55 mph
• has not occurred above 80mph (don't usually drive above that)
• occurs both while towing a small trailer and with nothing in tow
• usually begins as a shift point is approached, but continues after the transmission completes the shift (typically, shifting out of OD)
• happens much more often while going uphill than when going downhill (lots of both btwn Phx & Flag)
• if cruise control is set, it will go away on its own if the cruise control backs off the gas (like after you reach the top of a hill)

The thing I find most odd is that it ALWAYS goes away as I let off the gas (or cruise control backs off). I can get right back on the throttle and the noise is gone and everything is fine. There's no loss of power and other than the thumping I tried to describe above nothing feels different when it's making this noise. There is no handling difference that you might expect with suspension problems. Also, no shuttering that might indicate U-Joint or other transmission problems. There's no check engine light and everything in the "system test" checks out OK.

My mechanic (very reliable) has checked and found nothing loose underneath (including no slop in the u-joints). My wife has not heard it since we returned to Phoenix on Sunday (only in-town driving since then). I even did a test run on open freeway yesterday and was unable to reproduce it myself.

I'm at a loss now, scouring the interwebs to see if I can dig anything up (I think this is the third Ford-related forum I posted on...). Anyone have any ideas about this?

 

ok i keep losing focus when i read that. what i'm getting from this is that your getting like a sucking noise at interstate speeds? and it goes away when you let off the gas? do you have a cold air intake?

 

No cold air intake, unless it came from the factory that way (I honestly don't know what a cold air intake is for...).

It's probably more like a rattling than sucking, to be honest. The wind noise inside the Expedition is horrific, and makes it really hard to pinpoint what I'm hearing. Plus it's been a week now.

We'll be on the road again next weekend. I'll take the camcorder and see if I can get some audio of the noise to clear up some of the confusion.

 

try banging on the exhaust system near the heat shields. or feel if the heat shields have come loose.