Conditional Formatting by Group within a sheet

Hello Forum.
I use this forum extensively for review and research yet I have never submitted a question before so hopefully someone may be able to help me figure this conundrum out .

I spent several hours researching and trying to figure out how to conditionally format my file to highlight duplicate data within sets of data within the sheet rather than within the (whole) sheet itself. I cannot find reference to application functionality which supports this so I think it may be a custom VBA thing; to which I have little experience with.

Although my file consists of 30,000 + records I have included a sample excel sheet of data show what it is I am trying to accomplish. My file consists of unique course numbers (col H) to corresponding descriptions (col G); a one to many relationship.... unique course# to several possible descriptions.

I would like to highlight descriptions if they are duplicates, but only by course number groups. So the VBA would look at the range of unique records in column H (course#) and highlight column G records (course description) if column G records are duplicates. When the course number changes; repeat. Make sense?

My intent is to be able to sort out the duplicates so I am left with only the non-duplicates for review. Otherwise I have to look at each record in my file to determine if an update is needed; yikes!

Again, thanks for reading and helping if you can.

Janell