Bike engines will make a variety of noises, hardly surprising with several hundred metal parts whizzing round thousands of time a minute.
If you are worried about the mechanical noises coming from your bike, then it's well worth investing in a workshop stethoscope. They aren't the doctortype with flexible tubes, but use a stick to let you delve into the middle of the engine.
They only cost about £20 and can save a fortune in misdiagnosis.
Start out by listening at different points around the engine, like the cylinder head valve caps, or the camchain tensioner mechanism.
An engine will often sound noisy on start-up because components aren't under load, the engine is cold and the oil hasn't warmed up and started circulating freely.
But then it should settle down to a regular beat. If a noise persists, or increases in volume, then that could indicate excessive wear.
Rumbling sounds are normally bearings in the bottom of the engine, perhaps the crankshaft.
A 'squawking' sound is probably the clutch wearing, while a metallic rattle that follows you shutting the throttle on a four-stroke means the camchain tensioner is worn.
A ticking sound from the top of the motor indicates that the tappets are worn or maybe the shims, depending on their design.
An erratic idle or a sense that the engine is 'hunting' could indicate a duff plug or the carbs or injectors are out of sync.
If there's a whining noise coming from the bottom end of the engine that means a gearbox bearing is knackered.
Finally, if your bike backfires or makes a 'spitting' sound, then there's an air leak around the exhaust headers or further down the exhaust system.