Thank you for posting the solution! I think my stuttering problems started after a windows update. I tried reinstalling the bluetooth drivers, did all my Dell updates, re-paired my bluetooth, tested wired headphones and all those didn't work.Uninstalling widcomm worked for me 
My DW1560 Bluetooth devices used work pretty well, but about a month ago it got really difficult to pair, and when I could pair, the volume/sound was quickly pulsating/stuttering or oscillating up and down. My Bluetooth devices worked fine on other devices, and audio out of XPS 8900 was fine through wire connected headphones and speakers. All software up to date/latest version. I searched online and uninstalled and reinstalled drivers and nothing seemed to fix it. After the last round of uninstalling and reinstalling, I started to get "Unable to start the Bluetooth stack service" at startup. I also noticed in Device Manager that some Bluetooth folders had warning signs and the detail/event history said something about not loading because a previous version was still in memory. Whatever. Then I found Rowzee's post of 5/1/18 about uninstalling the WIDCOMM Bluetooth driver. Finally found a solution which worked for me (XPS 13/Windows 10). I went to 'add / remove programs' and towards the end found WIDCOMM bluetooth driver. I removed it and system has been fine ever since.Rowzee Out of desperation and with no other option I did it. Now even my lousy sounding apple AirPod Pros work!  Thanks Rowzee and Dell Community!! I tried to reply to that post but couldn't. No warnings in Device Manager anymore and Bluetooth now works well on all devices. Does anybody know how this got messed up? Was it a recent update? Where did the WIDCOMM Bluetooth driver come from and when. Have I always had it? Glad it's uninstalled now!!
XPS 8900, Bluetooth, stuttering volume/sound after difficult pairing, FIXED