Need some advice from S650 owners running a Borla S-Type

[Addy]

I recently had a Borla S-Type cat-back installed on my 2026 Mustang GT (non-active exhaust). During the first day or two, I noticed a fairly noticeable low-frequency vibration in the cabin. After 2-3 days, it has improved quite a bit, but I can still feel a mild vibration.

Here's what I'm experiencing:

• Mainly around 1,600–1,900 RPM.
• Most noticeable under load (when accelerating after slowing down or rolling back into the throttle).
• I feel it mostly through the floor and center console, with a slight vibration in the seat.
• On the highway, I can hear a low-frequency hum in the cabin.(without music but not bad)
• No metallic rattles, clunks, or scraping noises.
• The mirror only vibrates very occasionally, not constantly.(if revved really aggressively above 5k)

For those of you with the same setup:

• Is this normal behavior for the Borla S-Type on the S650?
• Did your exhaust mellow out after a few hundred miles?
• Or does this sound like something that could be improved by checking the exhaust alignment or hanger preload?

I'd appreciate hearing from anyone with firsthand experience. Thanks!

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