Extremely noissey Opti 135

I went out fishing with my mate who has a Haines Signature 5.4 with a 135 Mercury Opti on the end. He gave the skippers cap so I drove the boat all around Kepple Bay to check it out for him. The boat seemed to be a little heavy in stern but I put this down to the load we were carrying. What I did find was the amount of noise the motor produced. From 1100 rpm to 3200 the noise was unbelievable. It sounded like it was vibrating at an enormous load cycle. It was impossible to hear the radio and very difficult to hear each other. Above 3300 the sound level dropped a little but not all that much.
I also found the throttle lever was very hard to position at a constant rpm. The motor would increase or decrease slowly in rpm's even when holding the lever in a vice grip. It also seemed slow in accelerating from idle, needing lots of "forward stick". My mate was told by the service people that everything was normal. I am amazed to be told the noise was normal. What do you 135 Opti owners think of this engine noise, is it really normal? It is unbearable and makes a days fishing and cruising difficult to say the least. My own rig has a 4st 60 hp Mariner on the end and is really quiet and smooth.