I'm gonna chime in and sum up what everyone else has said just because I like to see my words in print
j/k
But seriously...I think it's time to replace your pin and charger just to be safe, it could be a problem with either one...depending on the maker and quality of your pen it's got an expected lifespan of 250-500 cycles with somewhere in the 300 and something's being the average. The fact the light never turns green worries me that your charger isn't working right because if it was and it was just the battery getting old, even most eGo chargers have some sort of cutoff feature to prevent overcharging or charging a battery that it not safe. I am thankful you haven't had any problems yet...and as someone else said, leaving your pen out in the hot sun this time of year, espeically under glass on a dashboard or something like that can wreak hell on those little batteries...most of them have the ability to operate in a max temp somewhere in the 120's fareinhight and don't store where above that temp either, it can literally cook them....not saying that's what happened to yours, just something to keep in mind.
I would rather give too much information and arm vapors with the power of knowledge than rob them of that power by keeping my mouth shut and let ignorance rule the day...even if you know this already someone else who reads this might not and it's there for that person so they can know too.
As for sounds....a "crackle" and "sizzle'ish sound is good in Kanger tanks, it means the coil is doing it's job...it's when you get a muffled hiss type sound with a nasty taste that it is time to change, clean the coil (if you have one that can be cleaned), or drop the pin in case something bad is going to happen. Don't let what I've just said scare you...trust me, you'll know what I mean if it ever happens, and with something so low power like a penstyle it is extremely rare for that noise to occur so you're fine
But I would seriously look into replacing your pen and charger with at least another pen and charger if that's what keeps you happy....if you're ready to move on to something bigger and better a Nautilus or Nautilus Mini with a Segelei mini is a nice 30 watt little set up, and yes by the time you buy batteries and a good charger for them its going to be somewhere between 60 and a 100 for everything but you'll have a nice setup that will go the distance and probably treat you better and last longer than another pen style and open up new wonderful vape possiblities the penset just can't give you...but then again vaping is a very personal thing and it's all about what keeps you happy and not what anyone else thinks will. Just my two cents with a nickel thrown in for extra thought....
All in all, happy vaping and best of luck to yah