Rear Shock Replacement?
 

I have a 2011 Mazda 3s GT hatchback. I took it in for my first oil change earlier this week. After I got my car back, I noticed a loud clunking noise coming from the rear passenger-side when I went over speed bumps. I took it back to the dealer and was told my rear shock absorber was bad and needed to be replaced.

The car has 5,000 miles on it and I'm a little surprised a shock can go bad so quickly. I hardly ever have rear passengers and never use my hatch. The dealer said there was no way to know the rear shock was bad until now since this was the first time my car was lifted (for the oil change) and the suspension was completely relaxed.

Has anyone had experience with a similar issue? Is what the dealer saying sound legit?

I have the 1st year Mazda3 and for the last couple years it's had a severe rattle in the rear, first on one side, then on both. The dealer made several tries at figuring out what it was and finally decided the shocks were internally defective. He also insisted there was no safety or performance problem and I should change them when it annoyed me enough. Money's tight so I'm not annoyed enough yet. Heck, it's been several years. I won't really be convinced unless I take the thing apart myself and confirm it. I've never seen any other car with this problem.

[Rant On]
I love the Mazda3 in terms of features and how it drives, and I hope the later years are better, because the introductory year is piece of junk. They used poor quality bearings- I've had early wheel bearing failures, idler pulley bearing failure, air conditioning failure and severe early rust out due to poor paint. First it was the idiotic center brake light that traps water and destroys the trunk lid, followed by the wheel wells disintegrating. The car was described as inexpensive, but it's been the most expensive car I've ever owned over 36 years of cars. Good engineering sabotaged by shoddy construction. Mazda? Never again.
[Rant Off]

if you hit a hard bump with that wheel it could have blown the shock - but it's under warranty, just have it replaced, this is not a wear item at 5k miles.

The dealer replaced my rear shock under warranty, but it didn't solve the clunking noise. In fact, a creaking noise when accelerating or coming to a stop began shortly after they replaced the shock.

I took it back to the dealer and they "tightened the suspension bolts", at least according to the documentation they gave me. I suspect they tightened the bolts on the rear stabilizer bar, and that solved the problem for now. If the bolts on the rear stabilizer loosened on their own at only 5,000 miles, there's no reason they couldn't again.

To echo Conrad's post, I've been disappointed by the overall quality of my 3. My passenger seat rattles over small bumps and vibrates on the highway at speeds above 65. I informed my dealer, but was told my seat doesn't rattle any more than the other Mazda 3 hatchbacks they have on their lot. Helpful.

letting the suspension drop shouldn't effect the shock... yes it extends it but that happens over big bumps in the road too (weeee).
Though reading that makes me wonder if there's a bracket, or the e-brake cable that got bumped when the suspension was low... which may now be rattling on something.
I doubt the stabilizer links loostened up, bolts don't just do that on their own unless they were not installed properly... which is not too likely.

As for the seat rattle, i'm sure it changed with the new model, but I know mine has some slop just cause it's meant to slide and it can't be too tight. I've found plastic and other parts that have rattle issues - took a long time pulling things apart, adding foam / tape etc... to place tension on the plastic panels to keep things from rattling. The seat itself I don't hear anything from.
If it's a vibration, there could be a wheel balance issue or something.