Weird vibration #2 around 27mph light throttle

[TPNml]

Hi everyone,

Back with another vibration help request. This time, I am getting a vibration around multiples of 27mph, with it being worst around 27mph. Here is more information:

• The vibration occurs under very light throttle (<10%, or using cruise control).
• I can primarily feel the vibration in my seat at 27mph (it almost feels like the suspension is bumping up and down), but it starts transferring to the steering wheel at 54mph. I can also hear the diff whine increase and decrease in sync with the vibration, sometimes even causing unloading/loading clunks.
• The vibration fundamental frequency is about 5.5-6Hz at 27mph (about 330bpm), and increases linearly with wheel speed (ex. 11-12Hz at 54mph).
• Doing some math, we can calculate that the vibration occurs exactly once per wheel rotation.
• The vibration is worst in 5th gear (1:1 ratio for my DCT car, and yes the engine is barely turning and not lugging), but is still noticeable in 4th gear at 27mph and 6-7th gear at 54mph and above.

There are a few things that are unique to my car as well:

• The car has ECS 95A rear diff bushings. I do not remember the vibration being present when I picked up the car from the shop, or on other trips I made afterward. There is noticeable whine from the diff, which I accept as normal.
• In March 2023, I hit the rear right rim on a curb. That wheel's suspension was knocked out of alignment, which was then fixed by a shop which found no additional damage. As of today, there is still no significant play in either of the rear wheel bearings, and the vibration persists even using crazy tire setups like both sets of front rims from my summer and winter tire sets.

First order of business is to get both sets of tires balanced and checked for roundness, although I do not think this is the issue. I need to figure out if this issue is worth solving.

[TPNml]

Update: found to have noticeable play when putting hands at 9 and 3 on the wheel and wiggling it (with a corresponding clunk). There is no play when wiggling the wheel at 12 and 6, or when wiggling any of the other wheels in any direction. Will update as service progresses.