Strange noise upon heavy acceleration.

[RDThompson]

I noticed an odd noise during heavy acceleration which I can only describe as a sort of "squark" sound. I have to cross three lanes of southbound traffic in a fairly narrow window in order to head north from my shop. I get on it pretty hard and as a rule I keep it toggled to fourth with the engine brake on when in the city. At the point where the truck shifts to fourth while still under load is when the noise occurs. I suspect the drive shaft trunnion bearing. I'll get a look at that in the morning. Just wondering if others have encountered the same. I'm near 98K or at least the truck is, so I am expecting some wear and tear issues to surface.

 

[Prairie Dog]

Kinda sounds like turbo bark since is does it when it shifts. Does it sound like a big beer can being flexed once or like someone hitting the bell housing or exhaust pipe with a ball peen hammer just one time?

OTOH, I didn't think a VGT could bark..

Scott

 

[RDThompson]

It sounds further back than the firewall or bell housing. I've never heard of a VGT barking either but then I'm always coming up with unique problems. I'll know something in a while, as I'm about to pull it in for a look see.

 

[RDThompson]

Well it is definitely not a trunnion bearing problem, It doesn't have one. It's a one piece drive line. U-joints are sound at both ends. It may be exhaust or suspension, all I can do at this point is keep listening.
Lest you think me completely spare, I work on a 3500 that does have a two-piece driveline trunnion and all.

 

[cerberusiam]

A VGT will bark and make all kinds of weird noises if it malfunctions or is force to stay small. Not a WOOF like the HE\HX's but more of a SQUARK or squeal. If it is happenng under heavy throttle and a shift point I would look to the turbo as the source.

 

[RDThompson]

A VGT will bark and make all kinds of weird noises if it malfunctions or is force to stay small. Not a WOOF like the HE\HX's but more of a SQUARK or squeal. If it is happenng under heavy throttle and a shift point I would look to the turbo as the source.

The turbo was replaced at around 33k. The slider apparently got stuck and kept the turbo from being variable. Is the noise a harbinger of failure or is it just a characteristic of the beast. I did try to replicate the noise but was unable in a straight line. It only does it from a standing start in a moderate left turn. It could be something that is being torqued during the turn I suppose. I may put the GO-PRO under the truck this weekend and see what transpires.

 

[cerberusiam]

If it ONLY happens in a left turn it probbaly is not the turbo unless there is somethign about that turn that is causing inteference. Maybe exhaust is loose and only cause problem in specific circumstances.

 

[RDThompson]

I was on a site today that is a quarter mile of smooth concrete in either direction. After I finished my business I went to the far end and tried to duplicate the noise. It appears to be a shield on the cat. after addressing that I was no longer able to replicate the sound. Apparently the stress and torsion involved in making a standing start and moderate to hard left with a bit of wellie in, caused the odd noise.
Thanks one and all for the suggestions and replies.