+1,

A rhythmic snoring sound ---- zzzzz, zzzzz, zzzzz, ---- is often the chain rubbing the FD cage. It often happens under load in higher gears, because the load flexes the frame and crankset moving the top of the chainring outward to where the chain rubs the cage. When the load is removed the chain then recenters to the noload trim you set on the repair stand.

This is easily confirmed by looking down onto the Chain and FD cage and looking form deflection as you pedal.

OTOH - if you're hearing and feeling what sounds like a gentle purring or whirring, it could be normal chordal action, which becomes more noticeable under load, especially in higher gears (smaller cassette sprockets). Better chain oils will mask this to where you may not hear it, but it never goes away since it's a property of how chains run on sprockets.

BTW- BB problems usually sound and feel different, more like creaks and clicks as the parts deflect under load.