older CDs have started to sound staticcy

I have been burning CDs for use in the car for a few years now.
Recently, I have been having trouble with some of the older CDs sounding
as if they are an FM reception on the very edge of the transmission
range, flits of static interfering with the sound. Here are the tech
specs:

Burned under iTunes 6.x
Dynex CDs
PIONEER DVD-RW DVR-107D
Set to burn best possible speed

These discs played flawlessly at first, but have in the last few weeks
developed this problem. My suspicion is either simple heat and cold
extremes causing the data surface to develop micro-fissures that the
laser is reading, or I wonder if the label adhesive might be the cause
of my problems? I really like the labels I created, it makes it easy to
pick a CD at a glance, but if these labels are the cause of the
failures, then I will cease using them.

Then again, I am not expert enough to know if it might not be something
else, and thus my posting here for broader consideration.

One last technical note: the Dynex brand of CDs I was using started
giving me increased incidents of coasters, so I have switched to TDK
CD-R media, and have been happy with the results.

jt
.