mikejavo

The crack happens only during a hard pedal on the 3 smallest cogs. It doesn't happen all the time, in fact it's very random, which makes me suspect it's only one spot where the chain may rub against one of the guides one the large chainring. There is no skipping, so I've ruled out wear, and the chain is new. The chainline appears to be straight, but I've tried 3 different BB spindle lengths, (113, 118 and 122.5 mm) to center it better. The front derailleur has also been adjusted and centered during each swap. I've also tightened the chainring bolts, (they didn't really need it) and went to a 9 speed (presumably narrower) chain.

The crank is a Shimano Deore Hollowtech tripple. I've considered placing very fine shim washers between the middle and large chainrings, to separate them a bit more. Has anyone tried this.

Any insight would be greatly appreciated. Thanks.

mikejavo

Following another thread, I decided to check if there is a wobble in the chainring. That doesn't appear to be the case.

alcahueteria

is the crack just a noise or do you feel it in the pedals. Is it like a slip, which lets your pedals kick forward?
if that's the case then you may need a new cassette. Typically, people don't catch chain wear until they need both a new chain and cassette, so if you just put that new chain on, and didn't put a new cassette on, then that's probably what the problem is.
the chain and cassette wear together, and won't mesh properly with a new one of either.

TrekDen

I had a similar noise once, and it ended up not being the chainring, chain, or bottom bracket. Believe it, or not is was the rear wheel bearings making the noise. What was happening is the noise itself resonating from the rear wheel through the frame material (aluminum), and it actually sounded as if it were right underneath me in the crank. Took it to the shop, and the mechanic used a stethoscope to trace down the problem. I'm not diagnosing this to be your problem, just another place to look.
Good Luck,
Denny