When I really put my foot into it, hard enough to get the supercharger whining properly, if I have the passenger window down and am driving next to something to bounce the sound back at me, I can hear a high-speed clicking/rattling (I say clicking because it's at regular intervals). It doesn't seem to change in frequency very much as the engine speed changes. Only happens under load—revving the engine in neutral doesn't produce the sound. Possibly-related things: the alternator bearings are whining at idle now, but aren't making any other noise as far as I can tell, and I have the clutch/flywheel rattle at idle sometimes.

Anything I should be worried about? I've heard that the supercharger bypass valve goes bad sometimes—could that be it?

 

Best check & see if your MINI has stored any codes. My guess is you are hearing pinging, possibly from running lean or bad gas. If that is it you will eventually hole a piston. You might also pull the plugs & see what they look like. How old are your plugs & wires?

 

The bypass valve is on the driver side and they dont make any kind of clicking noise even if its bad. I would take a look at the passenger axle or wheel bearing. Check the belt and pullys as well.

 

Have you ever changed the CV joints. Because they are speed related instead of RPM related I thing something to do after the trans instead of before the trans. You do not hear it when cruising because it is not under load.

 

No stored codes, unless it stores codes and doesn't light the CEL sometimes? Gas is 93 (I've heard the noise with Sunoco and the local brand) and if it is running lean it isn't enough to throw a code. Plugs could be going—the car has 75,000 miles on it, but I've only owned it for the last 6,000, and I don't have anything like complete service records. I'll pull the plugs and have a look tonight.

This isn't my video, but this is the noise and the situation it happens in (at 60 seconds in):
Passenger wheel bearing seemed okay last time I checked—after my commute home, neither side was hotter than the other. Could be CV joint-related, but I don't get any noises while turning.

 

that could be the cam tensioner. super easy to replace.

 

This appears to be a common problem. My 02 MCS also makes that tapping or clicking noise when I'm putting a load on the engine. Most noticeable with the pass window down while running alongside a concrete barrier.

I replaced my timing chain tensioner, belt/tensioner assembly, plugs, wires, even tried going up to a slightly higher oil viscosity. Nothing made any difference.

The good news is; as soon as the window regulator fails on your passenger door and you can no longer put your window down, the problem seems to go away.

 

I had the same problem. When I replaced the belt tensioner and installed an ATI super damper, the problem went away for good.

 

Based on personal experience with my '03 MCS and several threads on this topic, I can say the noise probably is due to deterioration of your crank pulley. The stock crank pulley has a built-in harmonic damper in the form of a hard rubber ring between the hub and the outer rim in which the drive belt sits. As the rubber ring deteriorates the outer rim starts to wobble, causing a rattling noise in the belt drive assembly. Replace the crank pulley ASAP because if it totally disintegrates the flying debris will cause damage to surrounding parts. While you're at it, you might as well replace the belt and belt tensioner, which are normal wear items. Several threads debate the choice among a stock crank pulley, an ATI Super Damper (a la Mr. Bean above) and an undamped pulley. I went with the stock pulley and have been quite satisfied for many thousands of miles.

 

im getting the same faint noise...under wot

i am replacing all my pulleys (crank, supercharger, idler as well as new tensioner assembly)

let you know if it goes away

 

The more research I do, the more I'm thinking crank pulley or tensioner.

 

Three things to check, tensioner, idler pulley & crank pulley. Your video helped.

 

I forgot to mention that along with replacing tensioner ECG, I also replaced my crank pulley. The tapping or clicking is still there. In my situation I suspect it is timing chain related or spark knock. It's a very faint sound and never gets worse so as the Beetles say "let it be"

 

My similar sound was belt tensioner related, replaced the whole unit and noise gone.