I can't work out what's causing the grinding noise in my drivechain! No noise whilst on the flat but nasty grinding noise as the road steepens and I start putting some effort in. Rear hub seems to spin freely as does the freehub and the cranks in the external BB. Any ideas?
Chain rubbing on the front mech, when you put the power down flex in the frame/chainset may be causing it to rub.
Your muscles crying out.
Loose rear hub allowing tyre to touch the frame under power?
Bottom Bracket?
Frame flex?
BB cups a bit loose? Chainring bolts? Rear qr tight? Pedals tight?
Is it worse in any particular gear combos?
As it happened when I was climbing I was on one of the lower gears so migt be the front mech; surprised as no problem on the previous ride. The chain was pretty dirty so cleaned that up and everything else incase something was sticking somehow.