DIAGNOSIS It didn't break, it's likely behaving as programmed. Weber has released firmware updates for the EX4 that intentionally changed the fan speed profiles, often making the fan run at higher RPMs more consistently to improve temperature stability and reduce flame-outs.
FIX There's no rollback option for firmware, so this is the new normal. The fix is an adjustment of expectations—the grill is now operating as intended by the latest software. The louder, more constant fan noise is a trade-off for (theoretically) more reliable performance, especially at lower 'Smoke' settings.
IF THAT DIDN'T WORK If the new sound is a grinding, rattling, or buzzing rather than just a louder whoosh, the increased demand from the new firmware may have exposed a pre-existing weakness in your combustion fan motor or its housing. In that case, the motor might be on its way out and the noise is a coincidence with the update.
HEADS UP Don't ignore new, truly mechanical noises. While the fan profile is louder, it shouldn't sound unhealthy. If it's a bad bearing or something is loose, running it could lead to a motor failure mid-cook. If in doubt, call Weber support—they have logs of what the firmware changed and can advise if your noise is within spec.