See pictures in posting below!

So this noise is getting to me now. My car is lowered with 18's. When driving really slow in 1st gear lets say, hitting even the slightest bump causes a clunking noise from the rear, most often the driver side. There are no noises when speed is increased or while cruising.

What should I check out first?

See pictures in posting below!

 

are you lowered on coilovers or springs? when you had the vehicle lowered, whoever did the install, did they cut the bumpstops? if you are lowered with springs it is possible that with the reduced height and bumpstops that aren't cut, the stops could be getting scrunched on the strut piston therefore giving you a clunking noise.

 

Why would there be spring spacers, it the car is lowered

 

I inspected the springs visually looking through the rim and noticed the driver side spring is compressed 'tighter' than the passenger side. I counted 7 coils at the bottom touching together and 6 on the other side...

 

Maybe you've already thought of this, and I know you said it sounds like its coming primarily from the driver's side... but at least check your spare tire area. I know at one point I had an annoying rear-end 'clunk' noise over every bump when I first got the car... the tire just wasn't in there tightly.

 

hmm, i suppose i can check that... but looking at the springs alone there seems to be something wrong... i never installed these, so previous owner could of screwed something up.

 

Yes, it seems reasonable to check those out, but the 'clunking noise' just reminds me of the spare tire. A slightly overcompressed spring shouldn't generate that type of noise.
I've since removed my spare... since I have no purpose for it. (Also gives one a tad bit extra space.)

 

good clue, i guess sitting lowered on 18's renders the spare tire a bit useless...

 

Any ideas? Take the tires off and inspect the springs... what else should I look for?

 

Thats unfortunate the spare/tools did not fix the problem. I would take it to someone rather than pull the car a part looking for a mysterious problem. Then if they break it, its there problem.