noise under dash

I have a 94 K blazer also,I am having the same sound coming from under the dash or under floor board. Wondering if you found anything out yet. Please let me know something thank you.

I recently had my truck hooked up to computer, code #43 came up. I was told it was my brain, is this true? Iwas also told it could be the knock senser could this be true? This is a new crate motor and rebuilt trany. Somebody please help me out thank you.

what year and model is it