Astroman,

What are your pressures? It could be that it is overcharged. 134 has a nasty habit of getting into sort of a "pressure runaway" condition. In a converted system you have to add just a little and give the system time to stabilize then monitor your pressures, then add a little more, stabilize and so on.

If it is overcharged it could certainly be the reason for your noise.

I'm certainly not a proponent of conversion, but if it is already converted and you can get the pressures right you might be okay. The R4 is not a real bad candidate for conversion. If you do have trouble from high pressure it is more likely to be the compressor than a hose or other components. At least that has been my experience.

Reverse converting would be a good step, by I wouldn't do it unless you just can't get things right with the conversion. Reverse converting is a pretty major project if you're going to do it properly.

Good luck,