You really have nothing major due on the service schedule until 100,000 miles, then its a transmission service and a couple other minor things like new spark plugs.
I would either adjust or have the rear brakes adjusted up, HHR's are known for having marginally effective self adjusters on the rear drum brakes, well OK...to be honest they just don't work, so have the brakes adjusted at every oil change or tire rotation.
The squeaking you are hearing might be a set of front brakes nearing the end of their service lives, they are equipped with a "noise maker" that will emit a screeching when the pads are pretty close to worn out. So have the front brakes checked and serviced as necessary.
The clunking is most likely the sway bar end links or sway bar bushings, they are the main culprits of the phenomenon called the "HHR Clunk", here's one of a few threads on the noise and its cures.
front end clunk
We won it, we won it, we won it!!! RDE 2/15/98
"Steam engines don't answer back. You can belt them with a hammer and they say nowt." - Fred Dibnah MBE (April 28, 1938- November 6, 2004)