I used to have the Ts-850 and used a Kam with it. Here is a website that tells about a mod for this problem: http://www.radiomods.co.nz/kenwood/kenwoodts850.html
"A common problem when using a KAM-Plus multimode with the Kenwood TS-850 or TS-450 occurs when the KAM-Plus is coupled to the Accessory-2 socket on the back of the transceiver, producing noticable distortion of the transmitted audio when using the microphone in SSB mode."
I think if you google this problem you will probably find a lot more. I don't really anybody modding their radio unless they feel comfortable doing so.
73 es GL!