Two nerve racking noises.
 

So I when 4 wheeling the other day and a day after I start hear these two noises and I can't find the source! Hoping I could get some help by fellow Blazer owners.

First noise: When I reach a speed of 5mph+ this noise starts to happen in the rear. It sounds like foil shaking in the wind, or like loud constant sparking. It happens when I give gas and coast. I've check for anything loose, or anything the looks suspicious but I have no leads.

Second noise: Just started this morning. When I drive this knocking sound appears. No, it's not from the engine. It appears to be coming again more from the rear. It's a really deep sound and it travels through the floor board of the vehicle. The knock becomes more rapid and heavier as vehicle increases speed (whether I'm giving gas or not). And vice versa. Again it's not the engine, everything is tight nothings hanging (that I can see).

So there are my issues at the moment. I hope I am specific enough, I could trying to record a video if it would help, let me know.
Any help or tips where to look would be greatly appreciated.


Thank you!

-Matteo

Also at one point when I went 4 wheeling I remember scraping my rear differential on hard rocky dirt. If that helps. That's the only harm I know of that I did to my car that day. Other than beat the crap out of it, so to speak.

Check the diff fluid may have leaked out
or broken shackle

check the diff and replace the oil, also check for play in the u-joints and give them a shot of grease. jack up the rear and check for play and smooth rolling wheel bearings.

Is your K5 lifted?

The sparking or blowing foil sound, would it be like a grinding noise? Squeaking scraping? Could you have a rock caught in your drum brake or in the backing plate?

For the knocking I'd check out your shock mounts. If you have been beating on the truck the upper mounts are apt to break.

newguy and war00:

I think I remember seeing my rear differential leaking oil, but I have to check.

70-K5:

It's lifted 7 inches. I'll check the drums. I think I remember seeing this round thing that broke, I don't know what it is. I'll have to look at it again.

Thank y'all a lot for helping me pin point the situation, I really appreciate it. When I get off work I will post a few pictures.

Okay well I can't post pictures from my Ipad and I don't have a computer. But I'll try to describe it.

So My rear differential does leak, I'll take off the over and replace all the necessary parts and see if something broke in there.

As far as rocks in the drum I can't see anything abnormal, but to be safe this weekend I'll go to my buddies gramps warehouse to jack it, removes tires and rims, etc. and check for rocks.

Now I did find a few suspects for the knocking. First up is the brake line for the rear drum. Now I don't know if it's supposed to be like this or not, but the brake line (or whatever) travels front the front, then to rear left, then to rear right, then from the rear right it fallows back towards the from and stops and sit loose on the cat :icon_saywhat: damn CA.... So I tied up that, [I guess useless?????], brake line which at the end has this long rod on it. So that might have been hitting the cat.

Our second suspect is this sheet metal that's bolted above the cat to the floor boars. On the side closest to the rear it's not bolted in. High speeds could cause the to flutter, so to speak. So once I find the appropriate bolt it will be housed again.

Third suspect. There is this useless (I believe) chunk of metal (which I believe used to be a mounting bracket for some mod) that slides in this loop that shoots out from under the floor board. So I took that **** off. It looks like a sideways U and on one side of the U it gets three times as wide as the opposing side and has two bolts in it.

One more thing that might be of concern is the both my rear leaf springs (first three from the bottom up) are all sideways. Is that of any concern???

Thanks again for all your help guys.

Are you ****ing with us?

Nope. Thudding noise still appearing and getting worse. Now brakes are lacking response.

Your leaf springs are sideways? Did I read this correctly?