RV Repair: Dometic Heat Pump (59136.821) Very Noisy, heat pump, cold air

Question
My Dometic Heat Pump (59136.821) becomes very loud after 10 to 25 minutes of operation. It happends on both Heat and Cool, but Cool seems to be louder. The unit seems to work fine (hot or cold air comes out) and then after 10 to 25 minutes, the unit starts making a very loud 60-cycle humming noise. It is so loud that my neighbor asked me to turn it off. It appears to be working even during this loud period. The only way to stop it is to turn it off and use it again after 10 minutes. Any suggestion? Thanks.

Answer
Chip, First you need to know what exactly is making the noise. Open the top and with it running wait until the noise happens and see just what is making it. After that if it is the compressor making it you may need to tighten the mounts. It may also be the compressor has been run with low power and has done damage to it. After you determine what is making the noise let me know and I can tell you what to do next. I hope this helps, Bill