It’s to be expected.
Every time you engage the clutch, the plates that are driven by the engine through the clutch hub, push against the clutch basket fingers that drive the rear wheel. When eventually a gap develops between the plate tabs and the basket fingers, it results in an impact force between the surfaces that will both deform the plate tabs and notch the basket fingers. The larger the gap, the higher the impact forces - and the higher the impact forces the greater the deformation of the plates and basket.
So they get louder and louder until the plates and basket are replaced. It’s a progressive process, reset only by the replacement of worn-out mushroom-tabbed plates and notched baskets.
The OEM clutch (on most models) has steel plates and a steel basket that initially have a small gap between them. Aftermarket clutch components that are aimed at the performance end of the market, substitute aluminum plates, hubs and baskets to reduce their flywheel effect. Aluminum plate clutch packs are about 1.5 lbs. lighter, but because they rotate half as fast as the flywheel, their effect on performance is minimal at best. The plate-to-finger gaps of these pruducts are often initially smaller than the stock tolerances when installed as a plate-basket package such as the Barnett-Nichols combo. However, aluminum is a softer material, and consequently more suceptible to impact-induced deformation that eventually leads to larger gaps.
There has been some innovation to try to address this durability issue, however.
For example, STM has tried to overcome this problem by increasing the number of tabs on each plate (and the number of basket fingers) from the stock 12 to 48 tabs. The intended result is to distribute the impact loads over a larger tab-basket contact area (lower psi) to reduce notching to the clutch basket fingers and mushrooming of the plate tabs.
Nichols Manufacturing designed their CNC-machined aluminum basket with wider basket fingers that results in larger finger contact area and consequently lower impact stresses, particularly when combined with their Barnett clutch pack where extra care has been taken to initially minimize gaps.
All the comparisons that I've read say that Ducati OEM steel plate friction material tends to outlast the aftermarket plates. In one case, 25,000mi vs. 16,000mi (Barnett). So, at roughly the same price, the stock plates seem to be the better deal.
Finally, keep in mind that when you mix steel and aluminum, the softer metal deforms preferentially and clearance gaps suffer, more than for steel-to-steel. So if you have a steel basket, stick with steel plates.
