I have a very bothersome noise coming from my '06 S40. I will try to explain best as I can. It is a very hard noise to describe......Must be in 2nd gear or higher, clutch must be engaged and you must be accelerating or have some restance. Pull clutch in and noise stops immediately. Rev engine with clutch pulled in while rolling and no noise. It also stops on deceleration. I have heard this sound (extremely low) with the bike sitting still in neutral and idleing. I could hear this sound from behind and the right side of the bike. Sound is much like something intermitantly touching inside of clutch cover or in muffler, but it is loud enough to hear real easily without a windshield and with helmet on and doing 55mph. Not a knock or a scrape. Maybe a rattle. I know this is a poor description of the actual sound. It is bothersome and I am afraid something is coming loose even though the bike runs fine. I have thought it was a spark knock, but have tried 93 octane and running with the choke on.....No difference. It is very loud today, more so than usual. Any ideas would be appreciated....Dan

Just to rule it out,... put pressure, downward, upward, sideward... on the speedo while hearing the noise...

Noise is much less today, as has been the case before, but it is still there. I got on my knees beside the bike and listened carefully. At first I thought it was coming from the exhaust, but not true, I covered the exhaust outlet with my gloves and the sound did not change. As I moved up the muffler with my ear, the sound continued, but dissapeared somewhere short of the front of the muffler. A better explanation of the sound is something like you would make with your mouth if you were trying to simulate a steamboat fog horn. When riding, add to that something like a mild clap on acceleration.  I am just about to believe it could be a deteriorating bearing having to do with the clutch or trans, Maybe it is just a normal sound for these bikes. Whatever it is, I don't like it.

As far as the speedo, I tried pushing it every which way to no avail. I also took off the side cover to the front sprocket and rode the bike without it. Same sound today with the cover on or off. Thanks guys for that info, but it is something else. Thanks, Dan

Take a long screwdriver & put the handle against the bone in front of your ear. Use that like a stethoscope.

Ed L. wrote on 11/15/09 at 13:17:07:


I will try your idea of checking the torque. How do you hold the pulley still while you torque the nut? Thanks, Dan

Strange as it may seem, I am beginning to think this sound may be something like detonation or spark knock. When I first got this bike, I had my mechanic friend do the white washer mod since it was running very lean and surging unacceptably. He ground off about half of the spacer. Surging is hardly noticible now and fuel mileage is around 57mpg. The bike runs strong. The strange thing is that when it was so lean, the spark plug was sooty. The idle screw was out about 2 1/2 turns. Can you explain that? I have not checked the plug since the modification.

During warmer weather, I had the idle mixture screw set at 1 1/2 turns out and all was fine except for that same old noise I have been complaining about. As colder weather moves in, I am getting more backfires even with more turns out on the screw. Still runs good though.

I believe the previous owner upped the main jet to a 155. Not sure what is standard for an '06 S40, but a 155 is what is in there now.

Oh, by the way, I even checked the airfilter to see if it was rattling. I sure appreciate everyones help. Please don't stop now. Thanks, Dan

I have a very hard deep knocking type of noise on WOT only, but only thru the intermedieate RPM range. Mite be spark knock,...I wouldn't know, but it doesn't concern me much if at all, because anymore, WOT is not my most favorite throttle position for more than a few seconds !
And seems like I had about the same noise on a 750 Norton Atlas years ago. The noise never changed.

i heard the same noise i think for the first time 2nite, i remember my friend saying detonation sounds like a death rattle or knock, mine was coming from the front of the engine.....

this is drivin me nuts as i'm not sure if it always has done it and i'm just now hearing it OR something is going wrong....but she runs fine...even 2 up!!