The carts I've got have 5 small cut-out grooves where it meets the battery ...... and the sound is more like a "ssshhhh" than a whistle !!I modified my 901 batts by cutting a groove through the connector to use cartos. I don't have actual KR8 batts. Sometimes with a certain cartomizer and a certain battery, I'll get a bit of a whistle. Is this the noise you get? I loosen the carto a touch and it fades a little.
I got blank black cartomizers at vaporkings.com and eastmall.net.
put a finger over one of the holes when you inhale
That's better than sucking through a tracheotomy from throat cancer!
I don't know if this will help but I use a 510 5volt passthrough with kr808d-1 cartos while inside and get no noise. Plus the mods I use outside are 510 connectors with the same adapter and no noise on them either.
My husband says I sound like Darth Vader from accross the house. Now, that's pretty loud.