Try to nail down the source / cause of the noise.

Here’s how:
Systematically eliminate possibilities.
Disconnect the FW cable... does the noise change or disappear
Disconnect the Motif XF from any external device, including USB, 5-pin MIDI... look for any change in the crackles
Disconnect the 1/4” cables to your speakers or mixer
Play the Motif XF with just headphones attached

Take note of when and if the noise disappears.
If you still hear it with just headphones attached you can eliminate a lot of grief.

Let us know.

Most common cause of crackles
Random crackles and pops are typically the audio buffer size on the computer not being able to handle the packet size of the audio it is delivered. The Buffer Size if too small causes crackles in the audio, here's how:

FW audio works like an old style bucket brigade... the Digital audio is placed in packets (buckets) which are passed along the chain to be thrown on the fire... digital audio is not a continuous Stream, it is delivered in a series of packets and reassembled at the destination.

Fill the buckets with too much water, and some drops will spill out before they get to the fire (the spilled droplets that’s your crackles and pops)...

This is typically solved by increasing the size of the Buffer (done in the DAW) so your computer can handle the incoming signal. When recording audio to your computer do not set the buffer size too small... the idea is to make it it as small as possible without any spillage.

Most users completely misunderstand this BUFFER SIZE setting... for the most part when you are recording audio via Motif XF FW, you do so monitoring a Direct. “Direct Monitor” lets you monitor with zero latency, that’s not a marketing term, it means you are listening to your signal BEFORE it goes to the computer. With an audio interface, like the XF, you don’t have to worry about latency... you don’t have to wait for the computer to process any signal because during record you can opt to listen to the source (not the signal that has been processed by the computer)

With FW, you never have to be at the latent end of the stick, unless you are recording using plugin Effects or are monitoring a computer based plugin. There is no need to worry about latency when recording your Motif XF, or any external device connected to its A/D Input.

Here’s how: Set your Motif XF to “Direct Monitor” during recording, and Mute the Audio Track in the DAW (to prevent doubling)
Then on playback, unMute the Audio Track to verify your results.

What is you Buffer Size?
What is your DAW?

Thank you for detailed reply. Pull out all the cables-- D'oh! I felt like Bill Gates told me to restart my computer... But after hours of hopeful troubleshooting/ playing and waiting for intermittent symptoms, negative result:
With just AC power (no surge strip) and headphones, still get crack-pops. Frequency might be less, est. every 5 minutes, and always very shortly after overnight startup (but not immediately after testing power off/on while in active use) .

(Had not been using with any recent FW, or active computer recording. Sketchiest connection likely was USB 2 into powered USB hub. Had 5-pin MIDI in/out of Yamaha arranger. Love 88-keys (XS) for piano practice- I'm 30 years behind in scales after misspent youth as a drummer. Record with Montage).

Thanks again!

Thank you for detailed reply. Pull out all the cables-- D'oh! I felt like Bill Gates told me to restart my computer... But after hours of hopeful troubleshooting/ playing and waiting for intermittent symptoms, negative result:
With just AC power (no surge strip) and headphones, still get crack-pops. Frequency might be less, est. every 5 minutes, and always very shortly after overnight startup (but not immediately after testing power off/on while in active use) .

Troubleshooting doesn’t change... oh but for the simple solution days of rebooting (fixed most early Windows problems — and all Windows support people would kick themselves if they didn’t request you do that first!) today rebooting rarely, if ever, fixes anything. Sometimes the noise is a misinterpreted ‘feature’

Here we have eliminated external devices, FW, USB, MIDI, microphones, and several hours of testing!

We’ve narrowed it to the noise can happen with nothing but headphones connected. The causes here can be further narrowed by now considering what specific programs are making the static. Are they supposed to or not?

Btw- eliminate the hub (Hubs are known culprits for trouble and many simply do not work properly).

Among the effects are Effect Type which are actually designed to make static-like results examples include:
“Digital Turntable” this Effect Type is programmable static... it recreates, with in depth programmability, the noise floor of a vinyl record. You can program click and pop density and speed, even how much dust is on the stylus. Very authentic sounding.
“Lo-fi” this Effect Type is designed to grunge the signal to where it mimics sample rates in the hundreds of Hertz. Low Fidelity, indeed.
“Noisy” by the name alone, you know this is going to sound rough and staticky; and a dozen or more Effect Types that purposefully add a noise/distortion component. Even the Rotary Speaker Type has an overdrive component.

Your task now, is to make a note of each Performance in which you hear the noise... I suggest just play through sounds and when you notice the static, simply write down which Performance it is... we can compare notes later. What we are looking for is — does this Performance include distortion, overdrive, static, etc., as on-purpose programming or is it a problem.

In addition to it being ‘caused‘ by an Effect Type attempting to recreate static on-purpose, it could be overloading the internal audio bus. It is possible to layer multiple sounds and simply distort the internal stages of the system.

If it is happening on User Bank creations only, then we know what to tackle next. If it happens on a Factory Preset and we review the Effects, we can then determine the exact cause — and then we can conclude if it’s a problem or a feature.

Let us know.

Re-loaded to factory presets-- static pops on Voices A01, A02, Performance A01, A02 [Full Concert Grand/Rock Grand Piano, Chilltronika/East Sider], plus other random factory Voices. No Effects edits. Test ended.

Okay, reconnect the Main Left/Right Outputs of the XF to you’re sound system and verify the same static noise is in the speakers.
If yes, you have narrowed the search and can take it in for repair, knowledgeable it is not computer connectivity, nor DIMMs, etc.

If no, then the issue is the headphones or the Phone jack on the XF.

Thank you ever so much for the personal, professional troubleshooting -- I would hate to have missed a simple glitch I had overlooked.
Also thanks for the many years of clear, supportive, and entertaining instruction.
Already spoken with certified care at the local level, will meet up tomorrow.