60 HP EFI Merc 4-stroke: WIERD noise????

[wharfcreek]

So this is about as hard to describe as anything I've ever encountered....period!! Been around 'engines' all my life, prior ASE Certified 'Master' Auto Tech (now retired).....and have some experience with boat motors, albeit not a great deal. So, with that, let me try to describe this noise: First, it seems to happen moments after a re-start. Shut the motor off and let it rest for a few minutes or more....then 're-start' it.......and for about 10 to 30 seconds, everything is 'normal'. Then, a faint, high pitched 'squealing' noise can be heard.....something akin to a high-pitched 'hiss'.....but more audible almost like a whistle. It also 'oscillates' some in frequency......bouncing around irregularly but still retaining the same 'high-pitched' level. It seems after a few seconds it even gets a bit louder. Then after doing this for maybe 20 to 40 seconds, it just dissipates and goes away. I thought that after a few minutes I might have heard it come back again....but still for only about 20 to 30 seconds worth.....and maybe not quite as loud. Then, gone! I didn't have an opportunity to try to remove the engine hood to try to get a more specific location of this noise....but if anyone is familiar with the sound you sometimes get from a solid-state 'switching' device......like that found in a battery operated electric drill when you pull the trigger. You can hear a 'squeal' in that too......until you pull the trigger all the way. This might also be somewhat similar to the sound some high pressure fluids might make when being pushed through a minute orifice. I'd say; 'think 'dentist drill' but that's too loud and frequency isn't quite high enough. Anyway...... I'm stumped by this......and wondering what might be a causal factor? Could this be an EFI related 'noise'? Something in the engine? I just had the boat on the dry-dock and did an engine oil change, a lower unit lube change, and replaced the water pump impeller. I don't have a clue if this could have had any effect on this....but I'll say I never heard this noise prior to doing this, nor did I hear it the first day I had the boat out after going back in the water. This is 'day 2' and I'm now hearing it. Odd!!! Anyway.....any thoughts, suggestions, or ideas would be REALLY appreciated!! Many thanks! Tom

 

[racerone]

How old is this motor ?----Perhaps check bearing noise at idler pully / belt tensioner if equipped with that.

 

[wharfcreek]

Just noticed that my earlier response seems not to have 'taken'. So, trying again. Motor is an '03. Due to inclement weather I didn't get much of a chance to play with the boat today, and what time I did get was spent doing some prop-swapping. But, in 'testing't he props, I didn't hear the noise. I hope to spend some more time on it tomorrow, weather permitting. Will follow-up with any updates then.