Ijust had boat yard change water pumps and thermostadts on my 2014 200 yamaha motors the starboard motor idles with a banging noise ,could it be the water pump wave washer
Where is the banging noise coming from, upper or lower section? Do both motors have the same noise?
Yes, bring it back to whoever did the work and don't run it until you know what is banging. I don't think it is the wave washer.