Scott,

There's a very easy to determine the culprit. First, plug another cable int the KP-100, but do not plug anything into the keyboard. Then jiggle the cable near the connection to the amp and if you get the crackle, the problem is with the amp's 1/4-inch female connector.

If you don't get a crackle, plug the cable into the keyboard, and repeat the jiggling procedure. If you don't get the crackle, then it's those new, custom cables. If you do get the crackle, the problem is likely in the keyboard's 1/4-inch female connector.

Though I've never opened a Tyros and looked at the connectors, I suspect they are ordinary 1/4-inch mono connectors--not stereo. But, even if they were, it would not make a difference when it comes to interference such as the nature you are describing.

In all the years I've been playing, I only had one incident where there was a problem with the 1/4-inch female connectors, and that was due to the accumulation of cigarette tars and nicotine in the inside of the connector. The problem was solved by cleaning the connectors with TV Tuner Contact Cleaner and a Q-Tip.

If your problem is being caused by the cables, which is the likely scenario, send them back and try another supplier.

Good Luck,

Gary