There may be worse problems that would require a service technician such as compressor issues. Refrigerant floodback occurs when the liquid enters in the compressor crankcase. This noise would usually occur should the compressor starts up. Another issue could be oil leaks causing a decreased oil level in the compressor but may well probably be pretty rare. It's more than likely the way your air conditioner is mounted that's causing it to make noise. Experiment along with the shims and I'll bet it goes out. Remember to unplug it from your electrical outlet before trying to do any internal work on it. . Most problems that people face with air conditioning units can be solved by simple maintenance and additionally cleaning. A regular cleaning of the air conditioning unit grille and filter helps to increase its longevity and make it more efficient at cooling. Sometimes particle aggregation inside air filter chokes the ducts and makes mid-air conditioner ineffective. This can be solved by way of simple cleaning of the air filter. The common problems with air conditioners are faulty a / c, collection of water pools below the air conditioning unit, rattling sounds when the unit is turning down, dysfunctional temperature control, etc. Some of these problems can be repaired by the owners themselves without calling for technical help. The air conditioner manual carries solutions to minor problems which can be easily implemented.Trane xr15 PriceTrane XL20i ReviewTrane xr13 PriceTrane XL14i Review