I forgot where I got this video from: [Wayback/Archive] YouTube Archived: private Dell video about detecting non-POST issues like motherboard or memory failures
It came in useful researching beeping pattern combined an amber/orange blinking pattern on one of my 2018 Dell 3060 MFF machines.
TL;DR
NOTE: On any OptiPlex built since 2012 (that is, 7010/9010/9010 AIO), Dell has stopped using all beep codes except for the Memory Failure code. (1, 3, 2, or one beep, then three beeps, then two beeps.) If your computer was built after 2012 and is making any other beep code, contact technical support for further help.
I knew it already needed a new coin cell battery, but that was surely not the only problem with it, and what type of battery it was (TL;DR: CR2032 and likely longer lasting BR2023 will be compatible too).
Related videos and links:
The Wiert Corner - irregular stream of stuff 