2000 LT 4dr 4WD - 80000 miles

Problem only occurs in 4hi

When foot off the gas and coasting I hearoften geta loud whiring sound not dissimilar to an air-raid siren. That is, the tone starts low, winds up higher and then slowlycomes back down in relation to deceleration. Immeadiately stopsif I step on the gas. 4WD deffinately engaged under load. Rear end just replaced by an excellent mechanic. (Whiring predated rear end failure) I use 4wd infrequently but it is needed from time to time. I suspect something is not disengaging properly when not under load. Any thoughts would be really appreciated.

 

To a certain extent, there will be a slight deceleration wail, but it should not be obnoxious...

 

Thanks for the reply.

Its not that. Just to clarify: This could happen when I'm halfway coasting down a 2 mile hill. Its not a siren sound but it undulates one cycle like a (wail) siren.You could almost recreate it by making a zzzzzzzz sound. Anyone have a clue?

Cheers

(paraphrase) "writing about sound is like dancing about architecture"

 

It could possibly be the front driveshaft U joints or something in the trasfer case ( I am not sure what would cause the transfer case to whine that bad (unless it is low on fluid, etc.))

 

Disconnect your vauum hose under the battery tray and see if the noise goes away. If so, your vacuum switch on the t-case needs to be replaced.

I had a similar problem. My noise was coming from the front end, and it was becuase teh front axle was partially engaged, if I popped it in 4x4 it went away, if I stopped or drove slow for a while it went away. It only came after I had been driving on the interstate for 30 minutes or so, and then decelerated. What was happening was the vacuum switch was failing. The engines vacuum was causing the switch to partially engage thet front axle, hence the noise.

Replaced the vacuum switch and I haven't had a problem since.

It woudl really help to know about where the noise is coming from, front back, left side, right side, t-case, etc. The more specific you can be the better we can understand the problem. You right though, discribing a noise with texxt is difficult. Got any way to post up a sound clip?

 

What you describesounds about right. I can't be more specific on location than to say when I'm in the driver's seat, it would be ahead and to the right...

The part you replaced looks to be about $50 which is half of what a mechanic will charge to spend an hour tracking this down. I'm not a fan of throwing parts blindly at a problem but my thought at the outset was this was an engagement issue and reading the threads here -- a common one. I'll get the part installed in the next couple of weeks and let you know how it works out. Thanks for the help