Hi Tom,
Besides looking at the VMWare environment configuration and making sure it's setup per our requirements(See APM Sizing and Performance Guide for details) key clue here is 10 minute interval between spikes,what you need to find out first is what's triggering that, are you running any Java Script Calculators\script on MOM or some sort of CLW query at same interval ? There are some known high Harvest Duration spike issues (usually happen every hour out of the box) that can occur when SOA Performance Manager extension is deployed or when SAN is used (every 5 minutes) but nothing similar. You might want to review below threads for more troubleshooting tips
-Enterprise Manager Performance Tips Interactive UI (https://content.plateau.com/nocache-content/ca/extended/product/apm/index.html)
-Top 10 Performance issues on EM (CA Tuesday Tip: Top 10 common causes for EM performance issues - Checklist)
If nothing helps then I would recommend opening a support issue with logs from all EM's and screenshots of relevant metrics so we can help you further.
Regards,
Kulbir.