Atari 5200 -- crackling, static sound

[Gapporin]

It seems to be El Día de los Muertos around my house. Between this and the fact that my Commodore 64 may be giving up the ghost, I'm afraid to touch any electronics for awhile.

I assembled and plugged in my Atari 5200 for the first time today after getting all the components together. I put the RF lead in my regular switchbox, and the power adaptor into the Atari itself (it's a two-port model, so it doesn't need the proprietary switchbox). Turned it on, and...was greeted by a loud static noise. Picture looks fine, but there is no [normal] sound coming out at all, just a loud "crackling" noise. I can wiggle the RF lead and the switchbox around to make it softer, but I can't get rid of it as a whole and I can't hear the actual sounds, either.

Is my RF lead busted, or am I missing something simple here? If it is the former, is there an easy way to replace it? Thanks in advance!

[Gapporin]

A small update:

I took apart the system today and sprayed the insides thoroughly with canned air. I found where the RF lead was connected, and replaced it with a known working lead. I even removed the RF shielding from the system, thinking that might be involved somehow.

No dice. I get the same results -- a more or less good picture, but unbearable static for sound.

Anybody have any ideas as to what might the problem be?

[channelmaniac]

Do you have a spare POKEY chip to swap out?