Before you jump into the macerator, check the hoses. They are the most likely reason for head smells. Take a clean rag and wet it with hot water. Lay it on the suspect hose and let it dry. Remove it and see if the rag smells. If it does the hose is permeated and needs replacement. The hose that doesn’t permeate and is very flexible is SaniFlex hose. I buy it from Defender, they sell it by the foot. No affiliation.
If you are one there is no explanation necessary.
If you aren’t one, there is no explanation possible.