Has anyone encounted an unusual deep ticking noise (too loud for a tappet yet too light for gudgeon or piston) in & around cylinders #3,5 can now be heard around # 4 & 6. Have lifted powerhead & checked cam chains & tensioner, tappets all o.k, sounds similar to a very very loud injector noise. Have listened to 2 other 225hp 4 strokes with not a hint of a similar noise. The noise has progressed from only intermittently when cold to all the time & seems to be getting louder. any ideas?