Assuming you just have one single tier server? (Mgmt, indexer and collector on same server).
You can reduce the threads used to index (idxwriter.exe) in Data Insight Servers > Server > Advancted Settings > Indexer Settings. You can also reduce the frequency, however this will impact how soon the access/scan data will appear in workspace.
You can also reduce the threads utilised to perform Audit pre-processing (Accessing events) and collection jobs in this way.
I would suggest you break out atleast the Indexer/Collector from the Management server, however you may need significantly more depending on your environment and how many filers/file servers you're monitoring.