Oh man, I know exactly what you're dealing with - that sinking feeling when you hear that 'expensive noise' and see conflicting error codes! Here's my go-to triage process to avoid throwing expensive parts at the problem:

1. First, I immediately power down safely and listen to that noise one more time. Is it a grinding, screeching, or knocking sound? Different noises point to different issues - bearings, misalignment, or mechanical binding.

2. For contradictory error codes, I always trust the drive over the HMI first. The drive is closer to the actual hardware. Check the drive's diagnostic parameters - current draw, temperature, and position error. These raw numbers don't lie.

3. Disconnect the motor mechanically if possible and run it unloaded. If the noise disappears, you've got a mechanical issue, not an electrical one. That just saved you from replacing a $5,000 drive!

4. Check the simple stuff first: power supply voltage, grounding, and connections. Loose encoder cables or power connections can cause all kinds of weird errors and noises.

5. Use diagnostic tools to monitor the feedback signals. If you're getting position errors but the encoder seems fine, it could be a tuning issue or mechanical backlash.

6. Swap components if you have spares - but start with cables and connectors, not the expensive drives or motors. A bad $50 cable can mimic a $5,000 motor failure.

7. Document everything - what the codes say, when they appear, and what makes them change. Patterns often reveal the real culprit.

The key is systematic elimination. Start with the cheapest, easiest possibilities and work your way up. That 'expensive noise' is usually telling you exactly what's wrong - you just have to know how to listen!