Improper startup can result in excessive temperature and radial loading, both of which can lead to lower pump reliability from problems such as seal and bearing failure. Consultant Ross Mackay describes the three steps that should be followed during pump startup.
That rumbling/rattling noise you hear from your pump is the symptom for any number of potential problems. The first step is identifying the problem. This article will help you determine what exactly is wrong with your pump.
Install a flow meter in the recycle, cascade the flow set point with a pressure control loop. With proper tuning, the valve characteristics are lost in the flow control loop, which should be tuned fast with PI.