150 hp opti, what is normal mid range noice/sound?

[psrl]

1999 optimax 150 hp s.nr.: 0G802873


There is an engine noice in the range 3200-3700rpm. Hard to describe, but it is a little "harder" than normal.
It have always been like this, and it goes away when I go closer to 4000rpm and sounds great....
Is this some kind of ressonance? Excess air from compressor?

Engine starts and runs great. Just curious about this sound....

Replaced reeds with glasfiber, replaced air injectors to the blue ones. Compressor rebuild last year...
Engine sound did not change after the upgrades.

[aussiejake]

My old 1998 135 Optimax sounded like a bucket of nuts and bolts being rattled around at that rev range.........was a great motor!

[psrl]

Yes I love the punch in that engine.

After som hard googeling last night, I found other raising the same question. In the comments section there was discussed that the newer, pre 2006 would be significantly more silent. Is this correct? And with what redesign? Is there anything I can do to modify my cowls, intake?
Already replaced factory noise canceling foam with heavyer foam and some kind of thin metal sheet on the top. (don't have the name of the foas, as it was leftovers from another boat :)

[Bulldog0156]

My 2005 Opti 150 has a lot of interesting noises if you pay attention to it. Runs great though so whatever.

[SilverFox579]

I'd think noise comparisons would be extremely subjective. As a hearing impaired veteran, my description of "normal" (and not just for my Optimax) likely would not match anyone else's.