Don't know if it's my C or D drive but the C records as being idle, despite being the boot drive, while the d drive is listed as active
What is telling you that?
Note that hard drives spin - that is how they work. If they have power to them, by default they always spin while the computer is awake. This is why they are often called "spinners", to differentiate them from SSDs which don't have any moving parts. If they were not constantly spinning, the performance of your system would greatly suffer as it would constantly be in wait states waiting for the drive platters to spin up to speed before any data could be read from or written to the drives.
If you mean the drive activity light on your computer case is constantly showing activity, that may or may not indicate an issue. A lot of stuff (OS "house-keeping", indexing, security scans, defragging, etc.) happen when you, the user, go idle. If you don't spend a lot of time on your system and you turn off when not in use, then it has more to do when you do power it on.