Goodman 2.5 Ton A-Coil pulsing.

[mooka]

Hi All

Got the duct work done for my A coil install, silfosed the lines, nitrogren pressure tested and gave it a good 30 minute vacuum. Upon start up, the dishcharge at the A-Coil give a noticable "pulse". Enough for it to make the line move. Right where the discharge changes to the orface tubes there is a built in bracket to hold the discharge line/orface tube assembly to the ductwork, this is something I have not noticed on any other installs. The system is r-22, pressures are 80/140 at about 17 celsius ambient temperature. 50 feet from condenser to A coil. The system is cooling just fine, the compressor sounds very smooth. Any ideas on what would cause this pulsing?
Thanks

[mooka]

Low refrigerant was the cause, added 5 pounds, ouch. Then pulsing stopped. Posting this to help anyone else with the same problem.