OK,

So here's the deal. As most of you know, I have 2 incoming CO lines. There's 7303 & 3942.

At some point (it may have been there from the beginning, I do recall making a post about a noise showing up and thinking it was caused by my alarm system) a noise started showing up on 3942. Don't quite know how to describe it, sort of a high pitched, very steady noise, present on 3942 at all keyset locations. You don't really notice it at all over the dial tone, but once you start dialing, you can hear it. It's not so loud as to make the line unusable, but just loud enough to irritate me.

I went down last night and hooked the buttset to the CO terminals. I then started pulling clips from the blocks, starting at the end of the chain and working my way back to the KSU, on line 3942.

Finally the noise went away when I pulled the clips from the first feed point to the 66 blocks, coming from the KSU. So my first attempt was to replace the cross connects going to, and coming from this point.

I Put the clips back in, and the noise was still there.

I then went up and diconnected the 2 keysets that were fed from that group of 66 block terminals... and the noise was gone.

Then I plugged one of the keysets back in. Noise comes back.

Unplugged it, noise went away.

Went to the other keyset location, plugged a keyset into it. Noise comes back. Unplug it, noise goes away.

Basically if I use a keyset on either of the cables supplied by the same group of 6 terminals on the 66 block, the noise appears.

Here's where it gets stranger. On the off chance I had 2 bad keysets, I grabbed a third. Same results as above.

Grabbed a fourth. Noise goes away, or at least so I thought. It went away from 3942..... but shifted over to 7303.

It was about 1:30 AM when I gave up, but a couple other things I did try was to repunch the 2 keysets at the block, which wasn't a lot of fun, but I managed to get enough slack to do it. The only place I haven't repunched is the KSU. Over the course of the night I also swapped out line cards, killed power to the intercom, disconnected the Melco C16, and removed the MOH and tuner cards.

I don't see how puchdowns could be the problem, since all keysets work fine, with no noise, as long as I don't use either of the 2 afformentioned keyset feed lines.

Any thoughts on the next troubleshooting step?

It's driving me nuts. Right now I just have them both unplugged and everything is fine on all keysets.

Thanks!
Matt