blocked radiator, sticking thermostat, cooling fans not working, not enough coolant or inefficient water pump
id be inclined to look at the 1st 3 options before digging into a water pump
sounds like the RTA "mechanic" doesn't know what he is talking about, as long as its below the legal DB limit, not to close to any moving or flammable parts, and secure there is no reason it is un-roadworthy