Well, a HIPS can be quite demanding
So far PrivateFirewall's HIPS has been the quitest HIPS I have ever used. I have received one popup from the always borked unsigned nvsvc NVidia service and that was it. Now I haven't turned on PF's Process Detection yet so the final verdict is still out.
At this point though, I would say that PrivateFirewall is a firewall with HIPS for the masses. The only configuration change was to set Network Security on the Home Profile to High since I am on a single PC. I also had to set Norton's AV and MBAM's applications to allow from filtered since PF's firewall was blocking some of the dial-outs.
Again a HIPS is only as chatty as you configure it. If your truely paranoid and set it to monitor everything including every outbound connection, of course your going to see a lot of alerts. You can then put on your tin foil covered hat and wait for an alien PC abduction.
BTW - Comodo in it's default Proactive configuation results in Defense+ remaining silent for the most part. The difference in HIPS between default setups of Comdo and PF HIPS is PF is still monitoring all critical OS files whereas Comodo's Defense+ will only do that if you set its settings to maximum ProActive. When you do that, you will see many more alerts. Finally PF has System Anomaly Detection which will detect application run behavior deviations from the norm based on a set percentage value. It's the only HIPS I know of that has that feature. A great way to catch a rogue process in the act!