Klarus XT11GT high frequency hissing sound?

Just got my klarus xt11gt. The newer version with the klarus IMR battery included. To other xt11gt owners, does yours have this hiss sound? If yes, I guess it’s normal.

I noticed that everytime I turn on at Turbo, I hear a very soft high frequency hissing sound for just around 2secs then it goes away. I only noticed it because I’m in a quiet room and I held it near my ear.
It only does that sound when newly turned on, if I turn it off then turn on again right away, there’s no hissing sound. If I rest it for a couple of secs/min to cool down then there’s that sound again.
I tried using another battery (olight), it doesn’t make any hissing sound at all.
I tried the klarus IMR battery on my BLF A6, I dont hear any hissing sound.

The hiss happens in electronics that have a frequency in human hearing ranges. Things you can do to lessen it is tighten the circuit board’s retaining ring.

same here, i have two examples here and they’re the same, i suspect that its normal due to the sheer amount of lumens out of such compact size light, while the older version of xt11gt that is way off the lumens spec did not have such noise.

unfortunately there isnt any retaining ring on this xt11gt design, its all fixed in place.

It’s called EMI and sometimes it randomly happens with a certain combination of power supply + circuit.
Same thing for PCs, certain combinations of power supply and graphics card will make coil whine.
It’s not a defect or anything and won’t cause any damage, just annoying.

Thanks for the replies.

@Keron and other new version owners, can you please check if when you remove the tailcap after the hiss/hum sound, if the tailcap and some also in the body has a very slight hint of burnt smell… it’s not too much just a hint of burnt smell or possibly some other electrical reaction smell. Thank you.

The driver uses a buck converter so it can hiss

Yes I do, but with my dog-like nose I can tell it does not smell like burnt plastic or any burnt circuitry, I attempted to dissemble the tailcap with a correct tool but no luck so far. But I feel like it wont effect the flashlight in the long run, hopefully.

Thank you! Yes, it doesn’t smell like burnt plastic, more like burnt paper or similar. You said you have several xt11gt units with you, is the slight hint of burnt smell present in all of them?

*additional observation, I noticed that mine’s beamshot tested against a white wall has a very small dark spot in the middle (doughnut hole as they call it in flashlight forum). Does yours have this?

Yes they do, and same as yours on the beamshot up against a white wall within 5 meters, but I suspect its normal due to the smooth reflector.

Same thing, mate, exactly the same. XT11GT XHP35 HI.

Thanks again Keron! and DMK…

I had the opportunity to test and compare another unit with mine,same updated 2nd version, it also has the Hiss sound at turbo and when I removed the tailcap it also has a hint of burnt smell. Both tests using the klarus 3100 imr supplied battery. Guess it’s normal, as long as everything works.

thanks for the confirmation, shouldnt be an issue in the long run.