Check your cabin air filters. I was at the parts store getting something else and it reminded me to look I popped the cowl cover and mine was nasty and it was only a little over 2 years old. Just a heads up for some of the newbies on here and a reminder to the vets.
this is the filter out of the 99 parts car with 156k on it
this is out of the 204k 97 gs
i will share a pic of the fiancee'* filter when I get a chance to dig into it and look it over
78 TTop TA w72,78 HT 4spd TA w72, 97 ws6 ta
03 regal gs 97 gs,06 gto, 93 blazer,98 k1500