You have a liquid cooler? Very few aircoolers use 2500+rpm fans other than stock and the 8700k doesn't include a stock cooler.
A aio pump will generally run @ 2500-4000rpm, so that would be normal, as would a 2000rpm fan on the cha_fan header.
If so, personally I'd switch the 2 cables, have the fan on cpu_fan header and pump on cha_fan header. Control fan speeds with cpu temps not case temps.
Which would likely drop temps a little.