Creaking bottom bracket. Solved.

New bike recently. A reasonably good Giant MTB with front switch off
suspension, hydraulic disk brakes etc. I use this as tourer, road
bike. Bike shop had to do a bit of kludging to get a carrier on it,
but they did.

Fine bike, except creak from bottom bracket, getting worse. Even with
knock.

Bike shop chap tells me that it's very unusual from BB. He's good but
I've been cycling for 50 years. I eliminate other causes. Get tool for
these cups on ISIS type BB.
Long weekend.
Find that my crank extractor pin is too narrow for this. It's a Race
Face BB. Nut taken off chainset. Need special crank extractor. Try 1c
coin. It bends. Eventually try bolt with head of correct diameter as
lever. Off.
Find that left BB cup is loose. Take cups off, grease everything. All
back on. Tighten.

Hey presto. As silent as an owl flying!