I am a 50 year old male with no history of serious illness. Recently I have noticed a slight crackling sound in my lungs with normal inhale/exhale breathing. Should I be concerned or is this normal?

Not normal. Should probably have this evaluated. If you do not have signs or symptoms of a viral infection / cold symptoms you may need a cxr.
Most . Most definitely not normal. Could be due to nightime gastric reflux causing stomach acid to go into your lungs or something more serious. I would be especially concerned if you are a smoker. You need to see a doctor and be examined, probably have a chest xray done.