Just finished sanding and stained one room. Noticed lines and drum sander indentations. Looking for a solution before I finish staining the rest of the rooms
https://share.icloud.com/photos/0McChRg ... Nw#Madison

The stain color looks pretty even on your picture. When the room has no furniture you will notice unevenness a lot more. It's not unusual to get some drum marks until you have more practice. The important thing when sanding is to keep a constant comfortable gait as you move forward. Any hesitation at all will create a drum mark. You can be aware of you forward progress and force a problem when it happens. To remove the drum mark as soon as it happens is important. If you go over the drum mark in another pass, you will elongate the mark across the floor. To remove the mark completely before you start another pass, you will need to sand diagonally in a criss cross pattern like a big X. This means that you will need to cross over onto the passes on the area you sanded on passes that you made before the drum mark. Once you take the drum mark out by sanding a few passes across the drum mark you will need to "spot" sand where you have made the X mark with the sander before you go any further with the same grit you have been using. This "dish mark" will not be noticeable when the floor becomes a lense as you look into it's reflection in bright light. Going over the floor with a buffer and screen can help, but if you have any hesitation in the sanding process when you have a sharp sanding paper will be noticeable as a drum mark.
Some sanding equipment can be especially prone to drum marks. The rental sanders that some places still rent out that have a universal motor that really gets running fast when the drum is not on the floor will cause a drum mark every time that the drum mets the floor unless you have quick reflexes and start moving pretty fast before the drum gets set onto the floor. With this type of machine you will have trouble getting a drum mark out without leaving diagonal drum marks, too. In this case, I recommend using an edger to remove these type of drum problems, but it takes more work to get a nice look.
It's great to ask for help after you noticed a "not prefect" job. It's lots of work to finish floors. I hope you can work efficiently and have good results.