A bloody canary in my engine (Whistle)

[Terroth]

As of recently my M20B25 has developed an extremely high pitched whistle, I've only had the engine running for about 3 weeks, as I just swapped it in to replace a snapped cambelt on my old M20B20.

The past few days this whistle has appeared, picks up after 1.5k RPM and i'm not entirely sure when it stops, generally around 4000 or 5000, but its mostly there under acceleration and not cruising.

I've searched high and low for this fucker, and using a homemade stethoscope (Out of a metallic grabby thing) I've located it to dead center of the intake manifold, quite literally right above the BMW Logo. I can hear it loud and clear there, but nowhere else along the intake system, as in if I go a few cm closer to the throttle body I cant hear it in the stethoscope, or either side of the manifold.

Is it ridiculous to think that the manifold has actually developed a hairline crack that i cant see, and is somehow leaking just the finest amount of air under load that it is causing a whistle?

I don't want to throw parts at this to fix it. And this thing has actually got me stumped.


*It doesn't seem to affect idle, its running somewhere between 600-700
*Doesn't seem to affect performance or cause the car to act funny while accelerating

[TobyB]

Tighten the 3 bolts, 10mm head, that hold the plate onto the intake in the center. 2 of them hold the bracket.

Thank John Parker.

t

[Terroth]

Cheers for the suggestion, but it was not the issue.
I tightened them and had no luck, so i bought a gasket sheet and cut one up and re gasketed it, no luck, used some carb cleaner to make sure it wasn't the issue afterwards. I inspected the inside of the intake manifold, and in comparison to my B20 one it appears a bit odd, the insides are not smooth, and there are strange scratches on the roof of the manifold, and odd folds (As if it was joined together) along the side towards the car, and not completely smooth like the others, none the less i don't think this is a contributing issue.


What i do have to show you is what it sounds like and what i discovered today muffles it...

Placing a hammer (Or equivalent solid object) seems to muffle the sound, the initial rev doesn't show it but others afterwards do, and I have tested it hundreds of times so it wasn't just a stroke of luck that it didn't whistle those times.
Yet, using my hand, or a rag etc doesn't do anything, wont change the sound at all.

Here, have a listen...

https://vid.me/8YNl

So....

What the flying fuck is going on...?

[TobyB]

Ha. The canary is intimidated by your big hammer.

Seems to me that something's vibrating, and the hammer dampens it.
And that hammer's big enough, and you're pushing it hard enough,
that you're probably moving the engine very, very slightly.
I'd go on a goose chase for anything loose, anything touching the
engine, and I'd also try tapping around when it was shut off.

And then I'd throw some corn meal in there, shut the hood,
and ignore it.

After changing the timing belt, of course...

t