Noise on shut off

[svr]

Hi all,
I've got a 99 M900 and just today i had an (unexpected) noise pop up.  It happens repeatably when I kill the engine by kill switch or with the key.  Bike starts and runs fine.  After shutting off I hear a low frequency squeak.  Sounds like as the final stroke is happening, right before the bike goes completely quiet.  It sounds almost like a large brake would sound like on an 18 wheeler or something.  not that loud, but that same kind of low frequency brake howl.  If you are a mountain biker, and you've gotten some mud on your rim brakes, you'll get brake howl kinda like this.  that's the best way i can describe it.  sounds like something coming to a stop.  fwiw i just installed some pod filters don't know if it could possibly be related.  it's loud enough that i can't quite locate it yet, but will investigate tomorrow.  can a dry clutch spinning down howl like that if say you just cleaned your bike and got some kinda cleaner in there.  im just nervous.

EDIT: I also just installed TPO crankcase breather filter directly onto the breather.  I found one post where someone mentioned you could hear some kinda noise on shut down due to pressure equalizing through the reed valve.  I actually thought it sounded like a high pressure squeaking through rubber.  i shall experiment tomorrow with the stock breather tank.

any ideas?  thanks!
steven

[Drunken Monkey]

Try the "poor man's stethoscope"

Get some plastic rubber tubing (like the sort you use to bleed brakes) stick one end in your ear (clean it first) and use the other end to narrow down where the sound is coming from.

The tube makes it so you'll only hear sounds from a narrow area, so first try the tube near the reed valve when shutting down, and then try a few other places and see if it's much quieter.

Generally this works well when trying to narrow down sounds on a running engine, but it should work for this as well.

[svr]

excellent idea, will do!

[Raux]

drucken monkey, are you thinking bearing? that's what i'm thinking. a bearing somewhere.

[svr]

99% sure it's the TPO crankcase breather blowing off.  I'm going to connect a length of tubing to it tonight and see if the frequency changes. 

[Drunken Monkey]

I honestly have no clue without knowing where the sound is coming from.

Sprag Spring / Flywheel spacer is my long-shot bet. Mine got misaligned by an idiot mechanic (me) and it would make a nasty noise at start-up and shut down.

[Drunken Monkey]

Anything to report?

[svr]

Not yet. I got sidetracked with wiring up some gauges. I'll check it this weekend and give an update. I may try to record the sound. It might be cool to have a thread where we could post sound bytes and solutions to the prob.

[CCEMN1]

Mine started to do the same thing when I canned the box & went with a K&N crankcase breather. My bet is, it's a pressure equalization thing.

[svr]

Anything to report?

Yep, it's the crankcase breather.  I attached to a length of hose and repositioned the breather so it's not directly on the case.  The noise is dampened quite a bit, but it isn't silent like it is with the breather box.

[CCEMN1]

Yeah, I think the key is, the noise happens immediately AFTER the engine stops spinning. That was what made me realize it was a vacuum noise & not a bearing, or anything more serious.