High IO CPU usage by WTCheck.tThread and WTJourn.Flusher

My MongoDB has been using so much io cpu recently. I checked iotop and I found these two processes using io cpu: WTCheck.tThread and WTJourn.Flusher. How can I reduce this io cpu? Will adding more RAM to the WiredTiger cache work? WTCheck.tThread peaks at around 99% CPU and WTJourn.Flusher uses around 1-5%. I’m using the EX4 filesystem but my host doesn’t offer the ability for me to change to XFS