Really odd situation with my sewing machine.
 

I use an older Bernina to piece. Yesterday it started to make a thumping sound. I changed the needle, cleaned out the bobbin area and stitch plate, put in new bobbin, and rethreaded. Still made the thumping sound. I realized the only thing different I had done was to change the brand of thread I was using. I thought that can't be it, both are 50 wt cotton. I threaded the machine with the thread I was using before and no thumping. Threaded the other thread and thumping started.
I did it three times and using one thread no thumping and the other thread thumping. Any one have any idea why?

Was the spool sitting level? You may need a little round scrap of felt under the spoon. Only think I can think of.

Was the spool/cone perhaps bumping again something when it turned as you were sewing. Perhaps it was the spool the thread is on. Do you have another spool of the same brand to try. Perhaps the 'hole' in the center of the spool is larger than your other spools and it 'thumped' as it turned because it was over sized for the spindle or not centered/off centered in the spool itself. I once had a spool that was off. It ended up being the center hole/opening of the spool was just a little bit oval instead of round like the spindle and it bumped against the spindle as the thread was pulled off.

I used the same thread stand for both. Both crosswound.

Maybe you need something like this.
https://www.ebay.com/itm/255831459374
It comes with my Janome machine and it holds the cone so it doesn't spin.
I think that's what causing the thumping.
I also have tiny ones that goes on top of small spools. Both very useful.

The thumping sound is coming from the machine, I can tell it isn't coming from the spool of thread. I called the Bernina dealer and the machine will be taken in. The dealer didn't seem surprised when I described the problem. Maybe she has heard everything. LOL

Did you clean under the
bobbin case? I had the issue yesterday and what a mess I found under the bobbin case.

Or just the bobbin case itself. For the longest time I had a Magic Bobbin Washer
in my bobbin case. One day it fell in the trash while I was cleaning the bobbin
case. Never bothered to replace it. Few months later I heard some rattling
and it was causing problems with my stitching also. After trying almost
everything I decided to put a Magic bobbin washer in there. Problem solved.

Ok, my curiosity got to me. What is a Magic bobbin washer? I had visions of tiny washing machines that "wash" bobbins. Silly me. I went down the goggle pathway and apparently they are real and of course Amazon has them. But I did find a nice explanation on the Leah Day site. https://leahday.com/products/magic-bobbin-washers Yes, it does sound like advertising but the concept does make sense. So, I have learned my one new thing for the day and can go back to bed. My day is complete. :) Magic Bobbin Washers, who knew!

I use the magic bobbin in metal bobbin cases. I started using them when Sharon Schamber talked about using them in her machine years ago. I still have a couple left in the original package. I've lost more than wearing them out. And the price sticker on back is $1.98 from a LQS. I'm glad I bought two packages back then.