which aw desktop are you using? a more straight forward way is to contact dell for maintenance service. (if it's still under warranty)

wait i think cpu will not make noise so i assume you're talking about the wc fan noise. have you tried clean up the rad? you can take it off easily and do the maintenance yourself.

if the wc unit is confirmed spoiled and not under warranty anymore, you can also replace the stock unit with third party units like corsair h55. (in terms of aurora)