Hi everyone,
I had posted about my planning to switch out my crank on my own, and after some good advice here and at my LBS, I proceeded. Lesson one: make sure your new crank fits BEFORE you take the old one off.... Yeah... Now I'm getting a new bottom bracket, because it's cheaper than returning a crank to Merlin in the UK. But that is a different story.
After taking the crank off, I just cleaned it, lubricated, and put it back in, since the new one did not fit. I also removed a broken washer that was just hanging on the arm, rattling, and didn't seem to have any mechanical role. Since then, on fast pedaling, especially with the chain on the big ring, I hear a regular purring sound, like bearing rattling, except it's not rattling, it's extremely regular and constant. Is this normal? Does it just sound like that because I've cleaned and lubricated it? The main reason I am concerned is that in the process of taking it off (it's an FSA self-extracting crank) I initially pulled in the wrong direction to take it off. I used a torque wrench to make sure I don't hurt anything even while taking it off, but I had adjusted it higher than the max specified tension to take it off (I figured it might need the extra push to come off), so I have definitely applied more pressure than specified initially, until I figured out I was going in the wrong direction. There is no other sign of malfunction, it spins straight and nice, but I want to make sure this new noise isn't heralding a high-speed on-road disaster.
Thanks!

Try removing the chain to isolate bottom bracket noise from chain noise. Was the broken washer perhaps a pedal washer?

The washer was on the actual crank axle, in the small space between the crank and the bottom bracket. Again, it was sitting there in mid-space, looking forlorn and useless... The noise is definitely from the BB, it was there very mild without the chain on, it's the same noise only louder when I pedal hard.

Washer sounds like a spacer to keep the crankarm out further from the BB. Since you removed it, any chance that the crankarm on that side is rubbing something?

Chains whine, whirr or purr, and it's a normal feature of all chaindrives. One major cause is the chordal action, or the effect of the chain effectively running on a 12, 13, 14...28 sided sprocket instead of a circular pulley. The difference between the high speed whine of an auto timing chain and the purr of a bike chain is simply the speed.

So purring is normal, and most pronounced when running on the slammer end of the cassette. Good chain lube cushions the small impacts involved, and quiets the chain, but some purring will always be there.

To the OP -- since we can't hear what you are and can't give you a specific answer, remove the chain from the chainring, and spin the cranks to ensure that there's no sense of bearing vibration. That way you know that you're hearing chain noise and not missing something else.

Thanks everyone. Yes, I did test without the chain, it seems to come from the BB-crank complex alone. However, there is no vibration to the hand, everything is spinning very solidly. Just, purring...

You MIGHT be hearing the effect of excess preload, or some other issue like rubbing someplace. There's no way to diagnose via the internet, so ask a knowledgeable friend to give it a look (or listen), or check with a pro.

Odds are it's nothing, but we can't give any assurance of that.

Each design is slightly different but that washer probably has a purpose. FSA has a wave washer to provide preload on the bearings. I suggest finding the installation documents for your BB and crank. The purr could simply be rubbing caused by a spacer washing missing.