Recently I've been getting this rattle. And by recently, I mean like the past few months. It didnt show up after any one repair, and I've wiggled everything under there that I could think to try and nothing feels loose. It sounds like it's coming from the trans tailshaft/transfer case...but there is no driveability or 4wd issues.

The sound is not really speed dependent..it is the same frequency and intensity despite speed/RPM. The sound does only happen at lower RPMs though. Above 1500 rpm or so it goes away and the car sounds fine. But even on the highway, if the RPMs drop around 1k it will come back.

The truck sat for a couple days without being driven (very rare for me) and it was noticeably louder and more continuous from 600 RPM to 1500 RPM.


Videos:
This is outside only, you can hear the intensity and see the speed relationship:
http://www.youtube.com/watch?v=ufbSdeAERwk



This is outside first, then I pull it inside so you can see the tachometer still with the noise.
http://www.youtube.com/watch?v=K1stoHwOsA8

 

It sure's hell doesn't sound like a spun bearing, or anything engine related. If it was, you would notice a loss of performance.

Thankfully you can duplicate the noise sitting still. Yet, the sound of that noise kinda scares me.

You, or someone else needs to go under to get close to feel everything while this is happening. A mechanics stethescope would come in handy to pinpoint where it is coming from. It almost sounds like a broken flexplate, but please, don't take my word for it.

 

glad to hear it doesnt sound like a bearing. I was hoping it wasnt engine related just because of how far back it sounds like its coming from, but I've never been around an engine that had a bearing or rod issue before.

 

Hey! That IS the wierdest,but isn't the adj. hardware for the back of the torsion bars about there? Does this fastener fail? Does it handle any differently? Sit higher on one side than another? How is your transmission mount? Check the tightness of the fuel lines that run down that side of the unit as well...Definitely let us know,Thanks step66

 

Somebody has played the old "zip tie around the driveshaft trick". Oh wait. in the second vid, you arent moving.

 

it almost sounds like the heat shield on the cat. converter has come loose. I dunno if your blazer has one But I had another vehicle that used to make that exact sound, even intermittently like that. I doesnt sound RPM or speed related from the video since it goes up and down even when you were outside the truck. I did see a bit of increase when you revved it a bit. check that heat shield. If that doesnt work, get it off the ground and use a screwdriver to your ear (mechanics stethiscope) and poke around in different spots. anything that loud should be easy to locate.

 

No it isn't the heat shield, that was my first impression when I read the initial post,but the noise is definitely coming from the left side of the unit. Another possibility(and I thought of this as I lay in bed reading last night) how about the trans cross member hardware? The fasteners that hold it to the frame? If they have been compromised you might have broken bolts raising **** inside the frame itself! But that issue would also be felt while operating the unit,as the crossmember wouldn't be doing its job to stabilize torque issues! As Jmooney152 said: If it's that loud,it should be evident with a good inspection! Please let us know what you find!

 

To me is sounds like either a heat shield rattling or it could possibly the catalytic converter. The internals may have broken up and are rattling around inside. i have seen that a few times and they sound similar to that.

 

Now that someone has mentioned it, it does sound like something is rattling around inside of a can, like the honey comb inside the cat is now broken all up.

 

the cat materials being the source of the noise would explain the lack of power i've been getting...


Been raining the past few days here in Raleigh, when it dries up I'll crawl under there and post up what I find. Thanks for the help so far guys