buzzing noise

I have read the other post that I saw about the buzzing noise coming from the what i am going to call the shift lever. This is my first boat the engine is a Yamaha pro v 150. I was taking it out for the first time. I have done all the pre trip checks. I have over half a tank of fuel, over 3/4 oil in the oil tank. I have put the mickey mouse ears on to check to make sure the water pump is pumping the water to cool the block. I get in the water and ride around and fish a little. When I go to load it back up I start it and it starts buzzing. I have no lights on and nothing to show me that there is a problem. I have three lights red, yellow , Green if someone can give me an explanation of what they signify that would be great. Back to the point the green light was on. So I am wondering why is it buzzing. It has a water pressure gauge but it seems to be stuck at 20. I am going to try to see if I can get it unstuck or replaced. But for now any ideas that would help would be great.

[boats.net]

Probably an overheat alarm, may need to replace water pump.

it seems that the buzzer goes off at lower speeds. Like at idle when I was loading up on the trailer it went off. From what I have read this seems to be a PRV. If that is correct could someone help me locate it on my engine. And maybe a short how to on replacing it and the water pump thanks for any help you can give me

thanks for the help but i am still a little unclear. Is it closer to the foot or to the top part. Is the water pump there as well.Thanks again

[boats.net]

It's number 21 in drawing, http://www.boats.net/parts/search/Ya...202/parts.html