...and I can hear the hard drive spinning occasionally.
Macbook Pros have not used mech hard drives since 2012 so that could be the fan which, in sleep, should be off.
In many Macbook Pros, magnetic switches sense the lid position and invoke sleep mode. If something magnetic is nearby, that could cause the computer to not be properly sleeping.
If the battery is swelling, that can prevent the lid from closing enough to trigger the magnetic switch. Battery swelling can be evidenced by:
- Uneven gap between display and chassis when the display is closed.
- Uneven gap between the chassis and the bottom plate.
- The computer rocks whe set on a know-flat surface. Solid-surface or granite countertops are usually reliably level.
- The trackpad bulges out.
LuckyLion21 wisely mentions other apps and processes. Are you running any anti-virus or so-called "cleaning" apps? Private network software (VPNs) can be problematic as well.
A sleeping computer is not "off" but in standby mode. The macOS has run automatic self-maintenance scripts for 24 years and those happen in the small hours of the morning. However, these run only for minutes and have never caused battery drain or heating on my Macbook Pros.