Pump noise is an undocumented feature. It indicates that the pump is running and may also indicate a leak if it continues to run when all taps are off. Can also indicate a slow leak if it runs for a second or so when all taps are off.
Be careful with the eBay seaflo pumps, a lot of them are fake and as such have no warranty, how do I know, I got caught that how. After a conversation with the Australian importer, I discovered that this www.ebay.com.au/itm/183863981870 is one of the few eBay sellers selling genuine seaflo pumps.