Fan speed will increase when new component installed on the server to provide sufficient cooling for the new component installed. Is the new card you installed on the server is bought from Dell? Can you share the part# of the card? Some time we seen this type of behavior when non supported card is installed on the server.  Which PCIe slot you installed the card. You can refer below link for type of cards supported in various slot [URL] 
Hi, I purchased the PowerEdge R540 three weeks ago and the fans was at 25% of PWM. Today I installed a 10G network card (10GTek X520-DA1) but now the fans are at 40% of PWM. There is no problem in the server and the temperature is the same (26 degrees). I know that I can change the PWM manually, but can I do something else before. The server was upgraded and I installed ESXi 7.0 Update 2 Build-17867351 (A03).  Thanks.
Ventilation too high after new NIC card