How can I differentiate between particulate in the sample, the sample probe, or the sheath solution?

If there’s particulate in the sample probe, dep. On the rate you flow it at. So change the flow rate and you will see more or less debris. If it’s in the sheath, it will stay constant because the sheath rate does not change. If after you clean the sample probe and you still have a lot of noise, it’s most likely in the sheath. If both are clean, if you have a lot of debris in the sample, you need cleaner buffers.