Blow off valve sound from rear?

[McM]

I just got my truck back from the dealer. Brought it for Transmission shifting, IWE and a squeak in the rear. 2020 with 43000 miles and it needed new rear springs. Of course they didn't find anything, but the springs. IWE noise goes away when shifting in 4AWD. All Vac lines are good. They replaced the springs and squeak is gone, It Lifted it like 1 inch and rides better. NOW.... I am hearing a lot of play in the rear, bunch of clunking starting and stopping. Now I also hear a sound every time I stop and it sounds like a Blow off valve noise coming from the rear..WTF.. Some research I found this below. Have any of you had this and had it fixed? What did they do to fix it?

Update.. plugged the vent and it's still happening. I can duplicate it by driving 200 feet at 10mph and coming to a 3mph stop then a big wooosh from the rear. Also what is this on the rear axle backside of rear brake?

A hissing sound from the rear of a 2020 Ford F150 when stopping, similar to a blow-off valve, is most likely caused by issues with the rear axle differential, specifically the axle seals or the axle vent; this noise often occurs when pressure builds up within the differential and is released when braking, creating a hissing sound.
Possible reasons for the hissing noise:

• Worn axle seals:
  The seals around the axle shafts may be worn, allowing fluid to leak out, which can cause the hissing noise when pressure builds up.
• Clogged axle vent:
  The axle vent, designed to release pressure, might be blocked by dirt or debris, leading to excessive pressure build-up and hissing sounds.
• Low differential fluid level:
  If the differential fluid level is low, it can also contribute to pressure issues and hissing noises.

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