just lowered it 3/4, now there's a noise in the rear.
 

2004 Blazer, 2door. just dropped it 3 inches in the front (coil springs), and 4 in the rear (blocks). put lowering shocks all the way around too. i now have a throbbing-like noise coming from the rear. it only makes it when the suspension floats/travels in the rear. saw that the bump stops were bottoming out, so i cut them out.... but that wasnt it. i got under the rearend just to make sure it wasn't the differential, and its not. i can lay under the truck and pull the body down so it makes the noise, but i cant find where its coming from. it honestly sounds like something is rubbing, but nothing appears to be. sounds like above the gas tank area, but nothing is visibly making contact with anything else. anyone had/seen this before?

Did you use drop blocks with the correct pinion angle, or any angle for that matter?

shocks
 

check to see if your shocks are rubbing on the leaf springs. Just something to check. The sides will be scraped up on the outside of the shocks if so. I met someone at a car show one time and they were talking about that and it took him the longest time to figure out what the noise was and it was the thicker part of the shock rubbing

check the sway bar i bet its making the noise, i removed mine. If not its your shocks bottoming out.

the blocks i used are angled. and i positioned them so that the lower end of the angle was facing the front of the truck.

i'm pretty sure the shocks aren't rubbing the leafs. i'll double check on that.

and my 03 s10 pickup never made this noise (and it had the same kit). do the pickups not have rear sway bars and the blazers do?

again, the noise sounds like its coming from above the fuel tank area. i've got under it a few times, and i'm pretty confident this is the area it's coming from.

II'm telling you its bottoming out the shocks.

I tend to agree with the shocks... the fact you used blocks to lower it means you didn't change the mounting points for the rear shocks right? Well if you put a shorter shock on than stock you could be over-extending them. I think this is what Brett is getting at.

Just for the hell of it, put your old rear shocks on and see if that solves the problem before you start pulling sway bars out and compromising handling.

Correct me if I'm wrong, (it's been a while since I've been crawling under the Blazer) but the rear mounting points are actually separate from the axle right? They're mounted to the bottom of the leaf springs. If that mounting point didn't change you shouldn't have gone with any shorter of a shock, maybe a stiffer one.

correct, the shock mount is a plate under the leaf spring that the u-bolts from the leaf/blocks loop over the axle. it makes sense that they could be topping/bottoming out. esp since i got some no-name brand as apposed to the belltechs i used on my other truck. the shock didnt look any shorter than the stock bilstein though.

hmmmm... maybe the fact they're no name shocks may have something to do with it.

Also, your tires aren't rubbing the inner fender well are they? Mind you that'd be a pretty ugly noise.

Keep us posted.

I would have to think shocks as well. If everything is installed correctly and tightl then thats all I would think could be the problem. I know if you go to low the driveshaft can rub on some trucks at the end of the cab just before the bed. I have never lowered a blazer though, only trucks. Its still something I would check if it only makes the noise when driving and not if you jump on the back.