I wish this was a post of good cheer....

Big Red is a 2004 F150, 4.6l, 4x4, that I bought in August with a 140k miles. It has always had what I'll call gear noise from the rear end, that is present when I use the accelerator and goes away during coasting. Presumably the thrust load on the gears/bearings causes the change.

Three weeks ago the ringing began, and this time the noise was from the center of the truck. The ringing occurs under acceleration, when the truck is cold, at speed around 30 mph and again around 60. It does not always occur, and when it does, it takes about 2 seconds for it to reach full volume which is pretty loud. When I let off the gas, the ring fades away over about 2 seconds.

I had the transmission and rear end inspected this week. The rear end checked fine; the tranny was full of metallic dust and needed a complete rebuild, including torque converter.

2 days later, the ringing is back. I will certainly ask the transmission shop to look at it again, but it has me wondering if the ringing could be from another source? It has a metallic resonance sound, higher pitch like a high C for those who are into music. Maybe a vacuum leak?

I'm stumped.

 

I wonder if you have a vacuum leak and the one or both of your front hubs for the four wheel drive are trying to engage at higher rpms you have lower vacuum pressure hence the let off the throtle and the noise goes away........ Just a thought

 

take a look at this thread
https://www.ford-trucks.com/forums/8...then-some.html

 

I hadn't thought about the IWE, but I bet you're right. When I first start the truck and then begin driving, the during the first 20 feet it seems like one of the hubs briefly tries to engage. The vacuum leak has likely gotten worse which is why I'm hearing the ringing when under acceleration. I'll check it out after Christmas.

Thanks

 

It could be the alternator or idler pulley or one of several things. Does it do this when it is cold out? Has it ever done this while it is in park or neutral or otherwise stationary?

 

It has not made the noise while in park/neutral. I'll make a note to check the pulleys.

It is rather inconsistent, sometimes it doesn't happen at all, other times up to 5 occurrences. The noise always comes in the first 5 to 10 minutes of the trip.

It seems vacuum related because it takes a while for the noise to spool up in volume, and then to decrease again once I let off the gas.

I stopped at the local autoparts stores for a vacuum pump and nobody had anything for testing the IWE. I'm ordering one on-line.