I dont believe that chromes "thump", at any age. I've used many sets of them for many years, and at differing ages, on different basses. They also dont "grind", IMO. To me, when new, they have a more "muted pianoish" tone, with fairly even tone across the frequencies. No particular frequencies stood out, except for a mild boost of upper mids. They were uncomfortably stiff and rough textured. Some of that roughness can be eliminated by scouring with steel wool pads, but there is still a sufficient gap between the windings that the testure can still be felt, and it is off-putting, to me. Even at several years of reasonably hard use, they will not thump. They simply lose their highs, which may be what the poster is perceiving.