So Prusa announces the new 400° HT hotend  in October, puts it up in the store but doesn't make it available for purchase. Obviously this would need to include a firmware upgrade and most likely a fan-shroud redesign but was this to just check off a box saying: "Hey, the Core One can do 400° now so get your PPS-CF on"? Wondering if the tested this in-house and melted the nextruder or something. 

I'm also assuming that this won't work with standard brass nozzles and will need to use exclusively the 500° Obxidian nozzles. 

Now here's the thing, if I print and the bed heats up to this temp, it's perfectly fine. Even after hours of printing. The manual heat up method throws the error within a minute. 

I print with ABS and I like setting the bed temp so that the chamber has time to soak up the heat since my enclosure is passively heated. It's not the end of the world that this issue is happening, but I was curious if anyone else has started experiencing this issue after upgrading the firmware.

The full setup is a Mk4, with 6.5.3 firmware, and an MMU3. 

   I’m reaching out to the community for help regarding my Prusa Core One L. I have been working with Prusa Support for about 2 months now, but despite numerous attempts and tests, we haven't been able to find a definitive solution to the following issues:

1. Persistent Ghosting/Ringing: Highly visible on complex geometries and test models. It remains consistent regardless of software calibrations or mechanical adjustments.
2. Asymmetric "Clicking/Rattling" Noise: Originating from the rear-left motor block. The noise occurs during Front-Rear, Left-Right, and diagonal movements (Front/Left - Rear/Right). It is reproducible even when moving the print head manually with motors off. I’ve also noticed that the clicking volume increases as belt tension increases.

Printer Specs:

• Model: Core One L
• Firmware: 6.5.3 (issue also present on 6.5.2)
• Filaments used: Buddy 3D PLA Black and other PLA filaments (prusa and no prusa).

Steps taken so far (under support guidance):

• Software Calibration: Multiple Input Shaper and Phase Stepping calibrations performed.
• Belt Tension: Checked and set within nominal range (92 Hz Upper / 88 Hz Lower).
• Axis Maintenance: Cleaned and lubricated Y-axis rods with Prusa lubricant.
• Pulley Troubleshooting: Swapped the motor pulleys between X and Y motors. This makes the clicking disappear temporarily (for about 48h of printing), but then it systematically returns. Grub screws are correctly tightened on the flat part of the motor shaft.
• X-axis Guide Rail: Loosened the screws, pressed the rail down, and retightened them from the outside toward the center as suggested by support.
• Slicer Profiles: Tested both "Speed" and "Structural" profiles and change speed and acceleration; ghosting remains evident, especially on faster profiles.

Video evidence and documentation:

I have compiled several videos and test files that clearly show the noise and the print defects:

• Complete Analysis (Photos, Videos and G-codes): Analysis Archive
• Click sound video (google photo link): Click video
• Ghosting Test with Buddy 3D PLA Black - HF nozzle 0.4 - 0.25 lyaer height - speed profile

Has anyone else encountered similar issues with a Core One L? The fact that the noise returns shortly after reseating the pulleys makes me wonder if there's a defect in the motor itself or an internal bearing in the left block.

Any advice or insight would be greatly appreciated. Thanks!

Is this a bad thermistor that needs to be replaced or is there some other trouble shooting I can attempt? This is pre-built system less than year old.