Mine has been hissing and sounding like a police siren for the last 5-6 years. Remapped also.
Pulls well and no errors.
Does not bother me anymore but people in the street will sometimes turn their heads :busted cop:
Short journeys with lights, radio, rear window demister on, cold weather.
Not enough time for battery to charge.
It's easy enough to remove with the right tools and if charger can fix it then I guess it's better than getting a new one.
I have contacted Tayna and described issue I was having. They responded with details on how to return the battery but also mentioning that battery might be simply discharged due to cold weather, short journeys, lights left on etc.
After advice from @NHN I have decided to buy CTEK charger...