https://youtu.be/yx9nCMKeIdw
Take a listen to a loose guibo bolt situation. Was yours taken apart and reinstalled? It's important to get the bolts the correct way and some use washers also critical.
Reused bolts can also throw off torque application and have the bolts not be tight enough.
My torque adapter is too large to fit in there so I need to use wobble extensions to get in there but it's important to torque to spec.
Use the likes of GoPro if needed to video while driving.
Persistence pays off you'll find the sound source and solution.
It's possible the sound is a shield getting hit by a rotating part that only happens from flex under engine braking. Look for things that are close to the drive shafts and telltale rub.
Also do some math:.
In the beginning of the video there is a very repetitive sound. Like tap tap pause tap tap pause.
Figure out the milliseconds between the pauses and you can calculate the frequency.
Recreate at a known speed. The differential is 4:10 or 3.91 : you can determine the rpm of the driveshaft and if it's a match it's drive shaft related even if pinion inside dif.
https://youtu.be/m78p41HBE-8
