Compressor Knocking Intermittantly - Broken Internal Mounting Spring

All refrigeration systems are sealed permanently and warranted by manufacturers against defects while under warranty. Once failure occurs after warranty, you have basically two options; repair or replace the refrigerator. Costs of replacing a compressor may not be justified when you find out costs. For now, all you can do is continue using it as is and anticipate failure. Search youtube videos on how they're disassembled and the inner workings to have an idea of what broke. The motor is lightly suspended to reduce vibrations, allowing a lot of free movement in normal operation. The problem is if excessive vibration will stress harden tubing to fracture it, rendering the compressor inoperative.

Thanks, I knew that. The question was Why does the knocking continue for 10-30 sec? And not every time? Some sort of pressure equilazation I suppose. Yes the quotes were around $300 for the compressor and $600 for labor and other misc parts. I would just replace the whole fridge but it's a difficult delivery.

Compressors have improved along with changes in refrigerant requiring changes in engineering. There are several types; rotary vane, scroll and the original piston. With a major change from r12 to r134a, some compressors may require redesign for optimum performance using the least amount of electrical power. My guess is compressors are smaller, outputting less volume while still being efficient with less noise. This can result in building up pressure slowly on startup and the noise you hear from internal vibration until optimum pressures are reached when vibration ceases. I'm not an expert on refrigeration systems but familiar with home and vehicle refrigeration and the changes made to accommodate environmentally friendly r134a. I may be completely wrong and welcome any correction from engineering experts in home refrigerators.