Hey all, I found this bit of info just now, needless to say, I'll be pulling the battery out having it checked out with a load tester.
A lot of folks post that their bike won't start but makes a fast clicking noise. This post is to explain what the noise is and why it happens.
The starter motor on a bike uses a lot of power to turn the engine. The starter button cannot handle the current that the starter draws from the battery so a large electric switch called a solenoid is used. The solenoid can always be found by following the heavy wire from the battery + terminal.
If the battery is healthy, when you press the starter button it sends a small electrical current to the solenoid which pulls in a contact with a heavy 'click' and supplies the heavy current to the starter motor. The starter is now connected directly to the battery and can crank the engine.
If the battery is not in good condition, or close to being fully discharged, something different happens. This time when you press the starter button it sends a small current to the solenoid which once again engages with a heavy click. This time however, because the battery is low on charge it doesn't have the capacity to supply the starter with the heavy current it needs but the starter is still demanding that current so it takes what it can from the battery until the voltage drops down almost to zero. Now the solenoid no longer has enough power to keep the contact in and it releases with another heavy click. This releases the starter load on the battery which recovers enough to once again energise the starter solenoid
and you get another click. As before, the starter load pulls the battery voltage down to zero, the solenoid releases and it clicks again.
The solenoid will keep clicking like this in rapid succession until you either release the starter button, or the battery becomes so flat that it will no longer energise the solenoid at all.
If you have this fast-clicking noise then firstly check the battery connections are nice and tight, as loose or corroded terminals can also cause the same symptoms. Next check the voltage across the battery terminals, or if you don't have a multimeter put a battery charger on the battery to build-up some charge. If after charging your battery for a while you still get the clicking noise there's a good chance your battery has come to the end of it's life and you require a new one. Try not to let your bike stand for long periods without giving it a top-up charge or leaving it connected to a battery tender/optimiser. Allowing a bike battery to discharge for any length of time can quickly reduce it's capacity.