Hi Simon,
The multichannel amps have sequenced startup to minimise the startup power surge, this is why the amps do a clickity-clickity-click on startup.
On the earlier design of the controller board it had the concept of a dirty relay that initially took the startup power and then a clean relay was turned on, followed by the dirty relay turning off. For the startup surge a single module creates this was somewhat OTT and was dropped in later units. Normally if this technique is used a low resistance resistor is in circuit with the dirty relay to minimise the startup surge and then the clean relay without the resistor is turned on a short period afterwards.