Buzzing Transmission? - 700R4

[NVBUYER]

Hey guys, I come to you asking for some help after both my mechanic and local AAMCO have been unable to diagnose an irregular noise.

Firstly it is:
-1972 K1500
-Carburated 350 H.O. (with a T.V. cable)
-4x4 3:08 posi rear & 3:07 front. The rear has new fluids and clutches, the front has old but okay looking fluids. I've checked the bearings and they have sufficient oil.
-NP205 (new seals, checked the internals, seemed okay)
-New driveshaft with new U-joints
-700R4 (Stage 2) from Bowtie Overdrives along with the torque converter
-4x4 adapter from Advanced Adapters

The engine and transmission have only 3,000 miles on them.

The noise starts to come on when the transmission is in 3 & 4 (overdrive) or around 40MPH in 2HI. It sounds like metal to metal from the outside, but in the cab it sounds like a buzzing noise that fluctuates regardless of engine RPM. It stay on for about 3-5 seconds and then fades away. It will return within about 30 seconds. If the noise comes on while I'm coming to a stop it stays until I reach ~5MPH. The noise does not occur when it is in park, or reverse. It solely happens when the vehicle is moving and usually when it is colder than usual (40 degrees or so). Some days its loud as can be and others it is completely gone. I am moderately confident that it is originating from the transmission area.

I know some of this is a little more knowledge than necessary but I thought I'd try to cover most of my bases. I have searched high and low on the internet and in town and nothing really seems to have the same symptoms as mine. Thank you in advanced for any advice you can provide me with.

[big bad orange]

maybe your flex plate cracked around the bolts? sorry I cant really help. TTT

[terry b]

Can you feel it in the transfer case shifter or the floor? How does the converter lock up?

[NVBUYER]

Originally Posted by big bad orange

maybe your flex plate cracked around the bolts? sorry I cant really help. TTT

Hello! Thank you for the response.

I thought that might be case but I figured the noise would be constant...? Not quite sure. Correct me if I'm mistaken. It's very harmonic (changes in tone) so I thought it might be something else. I'm trying to round up some opinions before I go ahead and split the block and transmission to check it out.
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[NVBUYER]

Originally Posted by terry b

Can you feel it in the transfer case shifter or the floor? How does the converter lock up?

Hi!

Yes, but you can actually feel it through the entire truck at the low end speeds. The torque converter seems to lock up okay, and also unlock (its wired into the brake light switch). Any hints on what I should try to pay attention for in particular? Thank you for helping me bounce around some ideas. I'm stumped.
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[terry b]

Could you find someplace with a chassis dino to put it on. You may be able to locate it better. I have no idea of the cost. Could it be a u joint?

[NVBUYER]

Originally Posted by terry b

Could you find someplace with a chassis dino to put it on. You may be able to locate it better. I have no idea of the cost. Could it be a u joint?

That's a good idea, I hadn't thought of dyno-ing it. It's just so inconsistent that it can't be predicted. I might have to let them hold onto my wheels for a day or two. Honestly its so annoying I think I could handle the cost.

To reply to the u-joint question: that's the first thing I checked. They're as tight as can be but I know they can loosen/tighten up as you drive (or so I've been told). They're new to top it all off.
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[terry b]

Hows the drive shaft angles?

[kaycee]

What about your pinion yolk bearing ?Does it do it when you have it on jack stands?

[NVBUYER]

Originally Posted by terry b

Hows the drive shaft angles?

I figured instead of trying to explain it I would just post some pictures. Hope these are clear enough.

[NVBUYER]

Originally Posted by kaycee

What about your pinion yolk bearing ?Does it do it when you have it on jack stands?

I had it up on stands about a week ago but I couldn't get the noise to reoccur. I didn't think about the bearing. I'll check it by the end of the week when it's supposed to cool off again. Thank you for the advice!

[SS Tim]

Might try a set of chassis ears to pin point the noise to the trans area. They narrow it down from there. Does the noise go away if the transfer case or trans. are shifted into neutral at speed?

[NVBUYER]

Originally Posted by SS Tim

Might try a set of chassis ears to pin point the noise to the trans area. They narrow it down from there. Does the noise go away if the transfer case or trans. are shifted into neutral at speed?

When the transmission is shifted to neutral it does go away. There have been some exceptions to that- when I'm on the freeway it sometimes stays around (but it could just be reverberating sound). I'll try it out Monday when I'm going to school to get a confirmation on that. Thanks for the chassis ear idea, I'll try to hunt a set down.