Rattling noise only when I add clothes gradually

Hi,

It just began, on my Kenmore series 80 dryer, the noise is inexistent if there are no clothes to dry as soon as I begin adding it appears intermittently then as more are added it becomes constant. it is a medium pitch rattling sound.

I opened the back panel, unhooked the venting tube, cleaned all the lint and dirt, checked for any lose piece inside the drum and everywhere I could see on the back, everything seems to be in order, I separated the heating unit and took a look inside the hot air conduct from where the noise seemed to originate, nothing there.

Any help, tip advice would be appreciated at that point.

Thanks

Ido