It's never a problem till it fails
If it's got noisier it means it's getting worse. A failed ISB isn't like say a flat tyre that you can just fix up after the incident. A failed ISB has the potential to litter the inside of the gearbox with its fragments. Consequently causing further damage to the rest of the box.
If the noise is getting worse and you haven't got any plans to fix it, expect your damage bill to be higher when it does fail.
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